This is something interesting. Installing the inetpub on drive C works, but the client wants it on Drive E. In putting on drive E, we got the 500.19 error.
We finally got it to work and the solution involves changing the identity on the SolarWinds application pool from NetworkService to LocalSystem.
UPDATE: changing the identity works temporarily. Once you run config wiz, the identity is changed back to NetworkService. The best solution I have found is from the kb: SolarWinds Knowledge Base :: What files and directories should I exclude from antivirus protection to optimize performan…
From the KB, assign the user NetworkService to the inetpub and that should solve the 500.19 error. Not sure why this is not set sometimes during an install. My best guess is maybe due to security restrictions on the logon from where the install was done.