INDIRECT.EXT and Windows Explorer

[Fergus]

I wonder if anyone else has had a problem using the INDIRECT.EXT function from the Morefunc Add-in. I have a workbook containing a number of INDIRECT.EXT formulae. It works fine. However, if I use Windows Explorer to open the File Folder where the workbook is saved, most times as soon as the cursor gets to the file, Explorer just closes. Another anomoly is that if I try to zip the file using Winzip, as soon as I click on the file to Add it, Winzip closes. Opening the file from Excel does not cause a problem. Anyone any ideas as to why this might be happening?