Excel 2007 : AutoRecover Error

[keems]

If I keep a workbook open for a little while I get the error: "An unexpected error has occurred. AutoRecover has been disabled for this session of Excel.

If I go into the AutoRecover options, under Excel Options>save, the AutoRecover options are greyed out. What's going on and how can I fix this?

Edit: It looks like the options are greyed out after I get the error, which makes sense. How do I solve the original problem then?