No debugging of VBscript
C1ReportDesigner allows the use of VBscript to modify the output. C1ReportDesigner is very particular about syntax, and it doesn't provide any error messages. And there are no debugging features. Quite often, the report will still be output, but the script won't work and you won't have any idea why.
If-Then-Else-End If Structure
This structure cannot be nested. So no If-Then within another If-Then. If you do this, the entire structure will fail.