“Error occurred while on Success script”.

Hello all,
I am receiving a log error message and I don’t even changed anything. I don’t know why got that error, I can tell you that it worked fine last week. I have no clue on why this error pops up all of a sudden.
Any advice?
Thanks.

Error details :
Error occurred while on Success script.
Error occurred while the inserting record (through addRecord task) into form Main Volunteer Core Scheduler.
The following field is unique
