Discovered an unusual problem with Outlook 2007

I have a client with an unusual Outlook problem. The application starts and runs with no issues, but it will not allow her to sort using the FROM or SUBJECT columns. Each time she tries she gets a generic error message – The messaging interface has returned an unknown error – and the sort fails.

If she sorts using RECEIVED or DATE everything works fine. I’ve tried removing and re-adding the column but that didn’t work.

Everything else in Outlook works fine. She can send, receive, use the calendar and every other function.

Has anyone seen an issue like this before?