Last night I fixed it by backing up SD files, reformatting, and pasting files back to the SD. It worked fine for hours.
I shut down the phone overnight, and today the photos and music files were again not seen by the phone. They are still on the card. I can view them, access them, etc. if I attach the phone to the computer.
The SD card is a full-price retail Sandisk 4GB microSDHC from Staples, not something off ebay.
I don't believe it's the card, and I don't believe repeatedly reformatting the card is the answer. Something else is going on.
Why does the phone stop recognizing the card? Last night I'd thought it was a conflict with Bluetooth File Transfer, because the problems began after attempting to send ebooks via bluetooth. Only the first book transferred, then it started with the "OBEX OPP Object Push Profile" problem, not being able to send files. The sending phone receives a "false" answer from the Xperia.
However, I re-did the card after that, purposely didn't touch bluetooth, and it did the same thing anyway.
The bluetooth may be caused by the same problem that's causing media to become unreadable.
It's so frustrating to go through all these problems on a brand new phone. I'm not a programmer but am left to try and fix it myself.
Where is the support? Where is the product testing? I did email Sony Support but have not received a response.