I also had the problem of Application Manager opening with the message Operation Failed. As I moved around Application Manager to make things better, instead things got worse. Any apps in Show Installed Applications disappeared; then I couldn't open Application Catalogue; etc.

Fortunately a Google ITT Search brought me to Makurosu's post which referenced ArnimS's account. (I put in the long first paragraph hoping it might help some future googler.)

I ran, I think as root, in Xterm

and all that appeared to happen was that I was returned to the prompt. But it magically fixed any corruption problems. No more corrupt App Mgr, happy me. Thanks, Makurosu and ArnimS!