Error processing internal candidate transactions

Summary

When processing promotions/transfers for internal candidates, the system errors out.

Content

When an internal candidate is sent over to "Manage Job Offers"and the recruiter goes in to process the necessary manual transaction for the promotion/transfer etc, the system is returning an error message that say "The assignment number already exists. Enter a unique assignment number. (PER-1530254)"

This is only happening only infrequently, some times they go through as expected. 

Does anyone happen to know why this happens or what to do when that happens? If you close the error message it will let you click Submit, but the transaction doesn't complete.