Hi everyone. First post. I have an existing workbook that is quite complex. It is an .xls version. One of the formulas is a sumproduct. This workbook all works fine, even when opened with Excel 2010. I tried creating a new workbook but when I used the sumproduct formula it says that it has run out of resources. I only used 4 cells to test the formula. I saved a blank file as an .xls instead of xlsx and it still does the same thing. I can't understand why the existing file which is complex has not resource issue with sumproduct but a new files with only 4 cells has a resource issue. Can anyone help? Thanks. kauzzie