Hi,
From workflow log(SWI1 Tcode) find out the step in which workflow is erroring out. Go to task of this method, navigate to the BOR or ABAP class method which is called. Debug the code to find out more about the error.
Can you provide more details about which step & how the error is happening.
Reason as we can see from the dump is that an attempt is made to create object reference for a class which is specified as a dynamic variable. But this variable is not filled properly & code is trying to create object for a empty class name resulting in dump.
Aspire