Partially used credit memo cannot be cleared

Hi,

I have a credit memo that was originally entered for $1404, it shows that $1392.66 was used on a payment a while ago.  On my Selected Payment register this credit memo is still showing as available to be taken but when I attempt to take the $11.34 balance remaining to be used on this credit the system will not allow it.  Has anyone else had this problem?  How can I clear this out.