Even if wallet says - "DB I/O Error" - wait for a coupl of minutes and run it again. Last week I`ve done it this way.
The wallet may crush again anf again, but you have to wait for a couple of minutes and try again.
IMHO, it happens then your system do not have enough RAM. So may be closing all the other programs (mozilla, google chrome, skype,icq and so on) will help you.