Hi bfraser,
I can't find the pivot table in the workbook.
In the data table in the first worksheet I see where you used a circular reference formula in column E. It evaluates to the "date" 1/0/1900, which is internally represented in Excel as the date serial number 0.
I was able to filter and sort column E on my computer using the drop down list in the column heading. Is that where you are having the problem?
I'm not sure why you need a circular reference. You can just put the constant 0 in those cells, and if formatted as date, it will display as 1/0/1900. I tried this change and still had date filtering options for the column and was still able to sort and filter.
Your formula in column F, by the way, evaluates to "1/1/00" (a text string) under certain conditions--not to a date. Also not that the if you enter a 2-digit year in Excel, it will be evaluated as the year 2000, not the year 1900 that your dummy date in column E is using.
You mention a userform. Does your question relate to it?
Asa