I'd download a fresh copy of the v7.7.4 upgrade archive from UBBCentral and then delete the install folder on your server and upload the fresh installer files from that new archive (FYI, I always upload the language files from the archive)...

My upgrade instructions are available on UBBWiki here and can differ from the instructions available at UBBCentral.

I am a Web Development Contractor, I do not work for UBBCentral. I have provided free User to User Support since the beginning of these support forums.
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