Auto Filter issue

Lately, I've been having problems with the Auto Filter feature. Previously it worked fine, but now it will just not filter on a couple of my spreadsheets.

Some background: The spreadsheets in question have around 200 lines. I am using Excel 2003 on Windows XP Pro and consider myself fairly proficient at Excel.

Here's what tends to happen: With Auto Filter on, a few filters may work, but eventually, I will click the down arrow to make a selection and nothing happens. To fix the problem, I have to turn off the Auto-Filter and then usually, have to select all rows and Unhide everything to show all the data. Then, I will turn Auto-Filter back on and the same process will start all over again.

This only started to happen recently and as far as I can tell only on a couple of similar spreadsheets with data in approx. 20 columns with a few VLOOKUPs in the data.

Any thoughts or suggestions?

Thanks

One thought that comes to mind is that the VLOOKUPs that you are using may be causing the problem. In the forumulas are the references locked to a certain range, or when filtering does the data range change, and therefore not filter because the results have now changed?

If that is not the problem are you able to post a copy of your workbook?