MIRO or currency issue

Hi,

Can you please help:

While creating credit memo against to the MIRO(  mrio has some issue so, want to create credit memo)  but  getting issue in balance field. 

Error: Balance not zero : 60.12 debit 211, credit 20.

I have checked in OB08 T code , i know that  this amount 60..12 because of currency variation.

please reply how to resolve this error.

advance Thank you so much for fast reply.