I thought you might be interested in looking at [Solved] Bad serial number with Steam install? Solution - Verify cache / Run as Admin.
https://forums.bohemia.net/forums/topic/97816-solved-bad-serial-number-with-steam-install-solution-verify-cache-run-as-admin/?do=findComment&comment=1645089
× Pasted as rich text. Restore formatting
Only 75 emoji are allowed.
× Your link has been automatically embedded. Display as a link instead
× Your previous content has been restored. Clear editor
× You cannot paste images directly. Upload or insert images from URL.