Updated Galaxy s3 and SD isn't recognized
There could be simple fixes that will allow you to keep your upgrade. With each new "flavor" of Android new APIs are released with relation to enhancements to the OS. Have you tried a brand new SD card? or backup and format for the current one?  Also a reinstall of the USB drivers may help. I hope you backed up your previous stock ROM because if not you will need to find one online(if possible). It will help if your device is rooted.  Good Luck!