If your phone is Sony-Ericsson and you see the following symptoms:

• Failure to download files via bluetooth (memory full)
• Camera photos are not saved

Do not reformat your card right away - it may not be guilty. The reason for such behavior may be the “read-only” flag set for some of your folders. Connect your phone to transfer files via USB and clear this flag for all files and folders on your phone and card volumes. Unfortunately this has to be done from Windows host system as I have no idea how linux vfat layer maps r/o rights to unix permissions, and I don’t care :)