I've removed the contents of the functions for brevity. When I run this, it works on the 1st run (everything fills in the cells and no errors), however if I click the same button again, I get an error saying I Googled and the results show solutions as releasing the objects via Marshal.Release (didn't work) and mentions multi-threaded apps, which I doubt my add-in is ... Unless it's running multi-threaded because Excel 2010 is? If so, how can I fix that?