I did a search for this issue, but it seems like it might be helpful to get a collation of possible fixes

I just got an urgent text from a friend to whom I'd given a Y200 I got as part of a contract rollover. She texted from work:

"“Can’t get messages. Phone is full, Won’t let me transfer onto memory card, although card has loads of room”

Any suggestions on things she can try, to address this?