Method not found: System.Collections.Hashtable DotNetNuke.PortalSettings.get_HostSettings()
If you get this error in DNN then you are having some major problems!
Method not found: System.Collections.Hashtable DotNetNuke.PortalSettings.get_HostSettings()
I spent a few hours this evening trying to track it down to find that my development environment was all jacked up placing DLLs in different directories. Which ended up causing me to do a build against an old DLL somehow.
To correct it make sure everything is setup properly and that your DLLs are building in the write directories.