Also the part about
Could not load type 'mojoPortal.Web.AdminUI.DatabaseManager'
Makes me think you are opening the web as a web site when it is meant to be a Web Application. The difference is that web application has a .csproj file which indicates what files are included in the project whereas a web site has no project files and assumes all files are part of the project. In this case its a false assumption as there is a file on disk for /Admin/DatabaseManager.aspx, but it is not included in the project. Its a stubb for something I never finished and could be deleted. There may be other files as well so its just not a good assumption. With a web application project all of the files included in the list in the project file .csproj will be compiled into a dll in the bin folder.
If you use the mojoportal source code and you use the mojoportal solution/projects then you will not get this type load error. Neither the mojoportal release files nor the source code for the web were meant to be opened in VS as a web site and it sounds like that it what you are doing.
For more info, google for "difference between website and web application project"
Hope it helps,
Joe