Simular problem, might have something to do with the VPP folder.
Make shore also that you do not have any old dll's anywhere that EPiServer will pick up, do a clean solution and manually delete all files in the bin-folder
I have upgraded a site from EPiServer CMS 6 R2 to 7.5 via Deployment Center. After running the "Upgrade/disable Add-ons After Product Upgrade" I cannot access the back-end/admin page.
Exception details:ActivationException: Activation error occurred while trying to get instance of type EPiDashboardController, key ""
Thanks in advance,