Cannot put games on R4 card

Hello

I have an r4-sdhc card

I got the card, put the software on.

then put the games on like super mario and mario racing, etc castlevania etc

They all work fine.

However, when I try to put more games on, It wont let me. What can I do ?

The only thing I can think of is, when I need to put a new game on, keep formatting the sd card. However , this is rather inconvenient. I did this and it worked, but its annoying. ANd I have to take the save games off the card, put them on my desktop, and put them back after I format the card.

But sometimes, when I want to put a new game on and I put the sd card in my computer it will let me put something new on, but sometimes it won't.

What can I do ?