We encountered the same issue following an install of v8.0 and was able to resolve it by removing the contents of /midtier/WEB-INF/platform/configuration, with the exception of the config.ini file. Of course, prior to this we verified that the correct jar files were in place.
While investigating, I noticed that logfiles were created due to the exception and within those logfiles, there were indications of a permission issue with one of the sub-directories, along with hidden files, in the configuration directory, NOTE: changing ownership did NOT resolve it. The MidTier was shutdown, I made a backup copy of the configuration directory and removed everything except the config.ini file, restarted the MidTier and we were back in business.
Hope this helps!