Cannot reverse Treasury transaction after F111 has been processed

My customer processed a money market transaction through to payment i.e. F111 was run, before realising the the deal was in the wrong currency. They reversed the deal via tm00 and re-entered it correctly. When the Treasury Accountant attempted to run TPM10 the deal was displayed ready for reversal, but when the reversal was executed, the following message was displayed: Payment request 10941 has been cleared: Reversal not possible

Message no. PZ096

In this instance, the error was realised before clearing on the Payment Request account occurred, so there is nothing to clear via FBRA.

Can someone please explain why this reversal is not permitted, or alternately provide the steps to reverse postings after F111 has been run in error.

thanks,

Chris