I don't see anything wrong with the step you provided., I modified the SourceSafe.bld sample (installed with Visual Build Professional) to use the same vbld_StepDone() event logic (with a simple "c:\out.txt" text file) and couldn't reproduce the error. Is there something significant about this out.txt file that might play into the problem?
Can you modify the SourceSafe.bld sample to reproduce the error and email that to
support@kinook.com?