There are many settings you can tweak with WSPBuilder. Type wspbuilder -help at the command prompt to get a complete list of them.
You can set these settings via the command line args, or a config file. To use a config file, create a WSPBuilder.exe.config file at the root of your project and add the settings to the appSettings section of the config file.
One of the settings that could be useful for debugging is TraceLevel. There are 5 levels as follow:
“0” gives no messages
“1” gives error messages
“2” gives errors and warnings
“3” gives information
“4” gives verbose information
The default value is 3.
These traces are written to the ULS. Use a tool like ULS Viewer (http://code.msdn.microsoft.com/ULSViewer) to monitor them.