The beginning of your stack-trace is informative:
C:\work\icade_svn\build_javadoc.xml:19: Javadoc failed: java.io.IOException: Cannot run program "C:\Program Files\Java\jdk1.7.0_15\bin\javadoc.exe": CreateProcess error=206, The filename or extension is too long
It seems there is good information related to this problem:
https://www.google.com/search?q=CreateProcess+error%3D206%2C+The+filename+or+extension+is+too+long
Including this potential work-around: https://stackoverflow.com/a/10598074/2736496
I hope this helps. Good luck.