Scheduled task fails with unspecified error at VB compile step

[philip]

I have set up a Visual Build project (using a registered installation of Visual Build Pro v5.0) that succeeds when I am logged in, but not when run as a scheduled task when no-one is logged in.

The operating system on the machine is NT4-SP6a with IE 6.0. I set up the build project to run as a scheduled task (and changed the command line from VisBuildPro.exe to VisBuildCmd.exe so that it should run without a logged-in user). The build project runs successfully when run interactively and also when the scheduled task is run while I am logged in to the system. However, if I am not logged in when the shceduled task runs, it fails partway through. The build is able to start, checkout some files from Visual SourceSafe, etc, but when it attempts to compile a VB DLL, it logs this error:

Building subroutine step 'Build DLL'...
setting version...setting project compatibility...building...Unspecified error

and terminates.