Thanks! It's a work around that is acceptable. The unfreeze fixes the issue. I can also 'refreeze' and it still works until I select another autofilter. Then I have to 'fix it' again.

The file is only about 500 lines x 9 columns but it's all text. Some of the text is pretty lengthy and it uses color coding and lots of links to other documents. Is it possible that it is a memory issue? (version is 2003)