The OnBase-HP web server's installation files and your OnBase Application Server must be restored from valid backups.
Ensure that the web.config files used by both your OnBase-HP web server and your OnBase Application Server are restored from the last-known valid backup copy.
If this is not possible, you can reinstall the OnBase-HP web server and the OnBase Application Server using their respective installers. Ensure, however, that you use the installers for the build of OnBase you are restoring (e.g., 11.0.0.31).