I found a workaround for this problem, since clearing cache and using incognito browser didn't work for me. Since the state withholdings were the problem, I changed the employee's home address and work location to an address in another state, then entered some placeholder data and saved it. When that succeeded, I then changed both addresses back to the correct ones. This caused the state withholdings screen to "re-set" for the correct state, and I was able to put the correct information in and save it successfully.

Good luck out there!