VBP captures the exitcode of every process it launches, and by convention a 0 exitcode indicates success and a non-zero code failure, so it's just reporting what it sees. First, verify that the same occurs outside of VBP. To do that:
1) check the 'Log the command-line...' checkbox on the Options tab of the InstallSheild action
2) build the step
3) Copy the logged command-line from the Build View
4) Open a text editor and create a new file in the form
<pasted command from VBP>
echo exitcode = %ERRORLEVEL%
saving as c:\test.bat
5) Open a Command Prompt and type c:\test.bat<Enter>
If the same exitcode is displayed, you'll need to open a support incident w/ InstallShield to detemine why it's returning a non-zero exitcode when it succeeds. If not, create a reproducible test case and send it to
support@kinook.com.
One workaround would be to mark the step to ignore failure.