The logFile argument in the job links on the JT jobhistory.jsp page is not properly URL encoded leading to links that result in 500 errors. I found the issue while working with the Cloudera distro which contained a plus ('+') in the path which is interpreted as a space character (%20) by Firefox. Here is the (trimmed) URL. Note the hadoop-0.20.1+152 directory which should be hadoop-0.20.1%2B152. I have created a patch against current ASF svn trunk but it is untested (although the jsp compiles to a class file ok).