There are a number of posts on this and other forums regarding this error. I've now got this problem and I'm not even writing any code -per se. Two pcs: one runs XP home with office 2003, the other runs Vista 64 bit and Office 2007. In the Immediate Pane of VBA on XP/Excel 2003 typing (without quotes) "?Application.MemoryTotal <Enter>" gives me the correct total of installed RAM. Typing exactly the same command in the Immediate pane of Vista/Excel 2007 gives me a Runtime 13:Type mismatch error. This is true for the other memory system properties of the Application Object eg memoryused, memoryfree as well as memorytotal. Is it a Vista 64 bit problem or something new with Excel2007? The problem was first noticed when I tried to run a project using these properties developed under xp/2003 on the vista/2007 system.