executed invalid operation during scanning

An update 

Hi, just thought I'd put an update here. I tried uninstalling both Reaper and EZdrummer, deleting the registry entries for both and then reinstalling both. Still no joy. I tried changing my normal account to an admin account and still the same. I think my next approach may be to reinstall whilst in the account I want to use. Anyone else have any ideas?

Hi Fabian, and thanks for your suggestion. I've reinstalled and moved my VST plugin folder to my Data (D) drive and, unfortunately, I'm still having exactly the same issue. Regards, James

A workaround / solution 

Just to update that I've finally managed to get this working with a workaround. I experimented with a test standard account and it worked fine so I completely deleted my old standard account and created a new one with the identical name and tried again and... Huzzah! It worked.