Why does MVN return -1 on successful build?

Question

I run Maven 2.2.1 and it returns the exit code from -1, although it claims that the build was successful. Does anyone know what causes this exit code as it violates our build process?

As one more concise information, MVN is called from our MS TFS build server, in which this problem occurs. If I can MVN from the command line, the exit code is 0.

Here's a summary of the reactors:

[INFO] ------------------------------------------------------------------------
  [INFO] Reactor Summary:
  [INFO] ------------------------------------------------------------------------
  [INFO] Aquarius Web App ...................................... SUCCESS [6.655s]
  [INFO] Aquarius Flex Library ................................. SUCCESS [1:26.329s]
  [INFO] Aquarius Flex Application ............................. SUCCESS [31.412s]
  [INFO] Aquarius Web Archive .................................. SUCCESS [5:22.484s]
  [INFO] ------------------------------------------------------------------------
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD SUCCESSFUL
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time: 8 minutes 34 seconds
  [INFO] Finished at: Mon Oct 25 10:19:50 BST 2010
  [INFO] Final Memory: 62M/225M
  [INFO] ------------------------------------------------------------------------