Hi,
I would suggest taking the mini sd card, placing it into a full size SD adaptor, then putting that into a memory card reader and running Windows Error Checking tool on it to see if it can solve any file system issues.
If that fails, then format the card using your PC, then place the card back into your handset and then perform a format from the handset.
Formating will erase all data from the card.
Transcend as far as I know are a reputable brand, but another well known mini SD card brand is sandisk.