When configuring certificates for a lync 2010 environment, I noticed that I made a typo. Failing to correct the problem via the topology builder, I had to uninstall the lync software. After correcting my typo, the installation failed to install. This was the error I got:
Opening the log file as mentioned in the event, it turned out I had something to do with an duplicate entry in the applicationhost.config.
As stated in the error it had something to do with a duplicate entry at line 421. Opening the applicationhost.config learned that line 421 didn’t had anything to do with lync. The trick was to find OCSAuthHelperModule:
After deleting this entry, the installation went perfect!