Battery Pack Issues

I have had my battery pack addon for 6 months now and untill today it worked perfectly on my 20D. Today when I had snapped off a few photos I got err cf on my display. I removed the battery and then the battery pack and ran the battery with out the battery pack and all worked well. I know others have had this issue so could you guys tell me how to fix this issue.

Its a contact problem...I had it once, did the same as you, and thats what I will try next time too...

Maybe contact cleaner?

Err CF is a card error. The grip might have triggered this if it's a bit loose and broke contact while the camera was writing to the card. But the general recommendation for clearing most error messages, regardless of the cause, is to pop the batteries, so just because removing the grip cleared the problem doesn't mean the grip caused it. Your card may have problems independently, or your battery might be low, or in the "wrong" side (one side is set to accept the AC adapter; I believe that's also the preferred side for a single battery). . . The "grip" issues generally surfaced with Err99 or complete total lockups not Err CF which you saw.