The Reference Manual section titled "CREATE DERBY AGGREGATE statement" makes the following ambiguous claim:
"An unqualified UDA name may not be the name of an aggregate defined in part 2 of the SQL Standard, section 10.9"
The term "unqualified UDA name" is supposed to mean the name of the UDA without any schema name. So if the full, schema qualified name of the UDA is MYSCHEMA.FOO, then FOO may not be a SQL Standard aggregate name like MAX, MIN, ANY, etc..
This was not clear during buddy-testing of UDAs. From the wording in the Reference Manual, the buddy-tester expected to be able to create an aggregate called APP.ANY.