** This issue will be addressed in ArcGIS 9.0 Service Pack 2 (SP2) **
If the last parameter in a model is derived, an extra comma is added at the end of the script. This is usually not an issue with Python scripts (as long as there is no more than one derived parameter), but it will cause VBScripts to crash.
This is a known issue.
** This issue is addressed in ArcGIS 9.0 Service Pack 2 (SP2).
Click on the link in Related Information below and download Service Pack 2, if necessary. **
If ArcGIS 9.0 Service Pack 2 is not available, manually delete the last comma in a text or script editor.