If you receive the attached error when starting up Outlook, it could be because of the following known reasons:
64 bit Office
If Act4Outlook is installed on an environment with 64 bit Office, then this error can be displayed at startup. Act4Outlook is only supported when being used with 32 bit Office.
Corrupt Act Installation
If the above scenario does not apply, this error could be caused by corrupt Act installation as well. In this case, it is recommended to first uninstall Act, reboot the computer, then reinstall Act which should fix this error.