I saw a similar failure, run against trunk classes sync-ed up to revision 963217, with ibm16 on windows XP.
The stack trace lines is similar but not exact; could be because of a differentce in revision.

testPing(org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest)junit.framework.AssertionFailedError
at org.apache.derbyTesting.junit.BaseTestCase.assertExecJavaCmdAsExpected(BaseTestCase.java:484)
at org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest.assertFailedPing(NetworkServerControlClientCommandTest.java:115)
at org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest.testPing(NetworkServerControlClientCommandTest.java:77)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:48)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
at org.apache.derbyTesting.junit.BaseTestCase.runBare(BaseTestCase.java:109)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)
at org.apache.derbyTesting.junit.BaseTestSetup.run(BaseTestSetup.java:57)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)

There is not a lot of information in the failure trace. This patch provides more verbose output with expected and actual exit codes and ouptut.

Committed revision 1081626 to add verbosity to the failure. I have not seen the failure running against classes with
java version "1.6.0"
Java(TM) SE Runtime Environment (build pwi3260sr9-20101125_01(SR9))
IBM J9 VM (build 2.4, JRE 1.6.0 IBM J9 2.4 Windows XP x86-32 jvmwi3260sr9-
24_69295 (JIT enabled, AOT enabled)
J9VM - 20101124_069295
JIT - r9_20101028_17488ifx2
GC - 20101027_AA)
JCL - 20101119_01

But I think others may see it more regularly. If it does occur, please cut and paste the new output in this issue.

I ran into this and it reproduced for me with insane classes with ibm 1.5. (sr12 fp3 + IZ94331):

There was 1 failure:
1) testPing(org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest) junit.framework.AssertionFailedError
at org.apache.derbyTesting.junit.BaseTestCase.assertExecJavaCmdAsExpected(BaseTestCase.java:513)
at org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest.assertFailedPing(NetworkServerControlClientCommandTest.java:116)
at org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest.testPing(NetworkServerControlClientCommandTest.java:78)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at org.apache.derbyTesting.junit.BaseTestCase.runBare(BaseTestCase.java:112)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)
at org.apache.derbyTesting.junit.BaseTestSetup.run(BaseTestSetup.java:57)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)

derby.log in the fail dir shows this:
Tue Mar 15 10:03:15 PDT 2011 : Apache Derby Network Server - 10.8.0.1 alpha - (1) started and ready to accept connections on port 1527

in the test dir it shows a (subsequent, I take it) shutdown as well:
Tue Mar 15 10:03:15 PDT 2011 : Apache Derby Network Server - 10.8.0.1 alpha - (1) started and ready to accept connections on port 1527
Tue Mar 15 10:03:43 PDT 2011 : Apache Derby Network Server - 10.8.0.1 alpha - (1) shutdown

This is sync-ed up to revision 1081628.

In my previous comment I must have missed a step in building. I sync-ed up to 1081864, clobbered, and built again, and I now get slightly different line numbers in the stack trace, but unfortunately, still not more info:

1) testPing(org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest)junit.framework.AssertionFailedError
at org.apache.derbyTesting.junit.BaseTestCase.assertExecJavaCmdAsExpected(BaseTestCase.java:516)
at org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest.assertFailedPing(NetworkServerControlClientCommandTest.java:116)
at org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest.testPing(NetworkServerControlClientCommandTest.java:78)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at org.apache.derbyTesting.junit.BaseTestCase.runBare(BaseTestCase.java:112)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)
at org.apache.derbyTesting.junit.BaseTestSetup.run(BaseTestSetup.java:57)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)

The line numbers had changed and I guess I was one assertion off. Added more verbose failure to the output assertion. Committed revision 1081884.

after sync-ing once more (revision 1082032), I now get the following output:

1) testPing(org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest) junit.framework.AssertionFailedError: Could not find expectedString:[Ljava.lang.String;@7c657c65 in output:Tue Mar 15 19:58:44 PDT 2011 : Could not connect to Derby Network Server on host nothere, port 1527: Connection timed out: connect

at org.apache.derbyTesting.junit.BaseTestCase.assertExecJavaCmdAsExpected(BaseTestCase.java:516)
at org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest.assertFailedPing(NetworkServerControlClientCommandTest.java:116)
at org.apache.derbyTesting.functionTests.tests.derbynet.NetworkServerControlClientCommandTest.testPing(NetworkServerControlClientCommandTest.java:78)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:60)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
at org.apache.derbyTesting.junit.BaseTestCase.runBare(BaseTestCase.java:112)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)
at org.apache.derbyTesting.junit.BaseTestSetup.run(BaseTestSetup.java:57)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)
at junit.extensions.TestDecorator.basicRun(TestDecorator.java:22)
at junit.extensions.TestSetup$1.protect(TestSetup.java:19)
at junit.extensions.TestSetup.run(TestSetup.java:23)

Modified the printing of the expected string with revision 1082305. Of course, right now, I don't see the failure (anymore).
Next time I see it I'll add a comment with the output.

This has not occurred for some time. Resolving Cannot Reproduce.