The question is 'what firmware are you using?' Is it the official acekard firmware or AKAIO. If the former than use AKAIO where I'll attach a link. Get AKAIO 1.8.1
If you're using AKAIO 1.8.1, than use the Anti-anti-piracy (AAP) feature by going into the main menu or going into 'rom settings' of each individual rom by pressing Y on the rom.
If you are using the AAP and aren't getting results than the problem is with your micro sd card. AAP is a new feature which is not yet perfected and should be fixed or improved with the next version of AKAIO, so you may have to play the waiting game. For more details on this, I suggest you go onto the Acekard sub forum on GBAtemp where there is a thread discussing this at greater depth...