Run the Cumulative update on your server then reboot in order to fix the ACCTivateApp.dll or other components.
Occasionally when starting up Acctivate following an update or new workstation install, you may encounter a message referencing a “Side by Side Configuration Error” that keeps you from being able to start up the application. The reason users typically encounter this is due to the present Acctivate.exe version not finding the version of the ACCTivateApp.dll that it expects. This can occur if the ACCTivateApp.dll gets locked during the install or update procedure – which can lead to it not getting updated and therefore mismatched. It can also occur if you haven’t rebooted your server since the last update.
How to Resolve
Simply make sure that all applications related to Acctivate (Acctivate and Acctivate Database Maintenance) are completely closed and run the install or update once again on top of the existing install. Even if you haven’t updated recently, run the last update you ran again. You do not need to uninstall and re-install. Once finished, reboot your workstation/server and try to log in again.
If the above steps do not fix the situation, please contact Acctivate support.