My phone shows SD card "read-only or not mounted" but it seems to be mounted b/c I can see files in Astro, but apps can't access the SD to write or play audiobooks, music, etc. I also cannot "unmount" using the phone, and running myBackup fails. I took the card to my pc and the card mounts fine as a disk drive and I backed it up, thinking I would format the SD, but the phone won't format because it is mounted and won't unmount. Should I format in the PC and what if so what file system do I choose?