An HTTP Error 500.19 - Internal Server Error occurs on servers on which K2 is installed that also has Windows Server Update Services (WSUS).
The XPress compression schema module (suscomp.dll), which gets installed with WSUS, is defined globally and loads in every Application Pool. Because the K2 IIS application XML is compressed, IIS cannot read it with XPress active.
Remove the XPress compression by following these steps:
For more information about this error see https://blogs.msdn.microsoft.com/webtopics/2010/03/08/troubleshooting-http-500-19-errors-in-iis-7/