I am using a Sandisk 2GB card in my Curve and it has worked flawlessly.
I also had a Pearl 8100 and upgraded to the 8310. I did not encrypt the card or anything of the sort. In fact, I actually saved some Media files to the card and moved them to my Curve, again without any issues.
Have you tried doing a hard reset? Are you running the most current OS on the Curve?
You can hard reset by doing a battery pull while the phone is on. To check your OS, go to options > about. It will look like 4.2xxxx.
I doubt that the hard reset would do anything but it's always worth a shot. If your OS is not updated, I would definitely do that as well. You can search on the Forums here to find step by step instructions for doing so. I had some minor issues with my Curve when I first got it but once I installed the most recent OS, I have had no problems.
"Once you go BLACK (berry) you'll never go back"