Is there any way by which we can debug the code written in the script workflow action?
Debugging and trouble shooting the Script Activities in workflow is a bit difficult. I have found using Try - Catch blocks with a WorkflowApi.TrackError() function in the catch helps. This will report the exception message back to the Messages tab of the Workflow instance detail.
Try
' Do Work ...
Catch ex As Exception
WorkflowApi.TrackError(ex.Message)
End Try
Usually for more complex code, I will start by developing the code in Visual Studio and then move it into Workflow after I have the code working properly. I still sometimes have to adjust the code in workflow, but the logic is known to work, so it is easier to tweak and make work.
Another thing I often do, although it is not really the "cleanest" way to debug is to add MsgBox() calls in the C# code and run it from the designer.
For example, I will add a try-catch and use the message box to display an error message in the catch block like MsgBox(e.Message).
Additionally, I might add MsgBox() at various points in the code to display the current value of variables to verify them or just so I can "follow" it through the process and see what gets done before it hits an error.
Another benefit is that the dialog window effectively "pauses" the script execution so I can use that to stop at certain points and evaluate the code before allowing it to proceed.