Try to reset the customisations of that report by just
selecting it and clicking on the Reset button at the
bottom of the list reports page.
- quote -

I am getting various problems with reports. The monthly
reports don't show up after I click on one. I get a
flash (dialog box?) that disappears and then no report.
If I try to do a spending by category, it
says.....loading.... and just hangs. I can go back, but
don't get the report.

Any ideas?