Mine worked fine for a while, too. I'm not sure what triggered it, but I think the phone did something to it. The reason I think this is simple. I have had many devices with SD cards in them, and never have I had one go bad. This phone was using a card that I had used for months before in another phone, and within a month the card was bad. When I looked online, I found hundreds of cases of the same issue, mostly with Samsung S3 and GN2 phones. It seems too much to be a coincidence.
Sent from my SGH-T889 using xda app-developers app
SGH-T889, rooted, CWM, debloated stock ROM
SGH-i897 build 1105, LANIGHT v6.5, Devil Kernel, Voodoo App (Backup)
HTC Aria CM7 (AT&T, sold)
HTC Wildfire(Bee) rooted, no ROMs (Alltel, sold)
HTC Touch Diamond CM 6.1 (WinMo, Alltel, sold)