1. Have you tried to removing the external card and reboot ?
Yes I have. I have unmounted, ejected, rebooted and tried transferring to just the phone, no luck. Re-inserted the SD and tried writing to phone and card, no luck
2. Have you by any chance activated the ICS encryption feature ?
Haven't touched ICS encryption at all. None of the ICS versions have allowed me to successfully write files to my phone. Pre-ICS allows me just fine.