The Problem :-

I had a problem with a very simple Intranet site which only had web parts in it and no variations when I upgraded it from MOSS 2007 -> SharePoint 2010. It failed with the error message "One or more fieldtypes are not installed properly".

After A LOT of investigations using reflector I found the following with the RelationshipList List. If I create a new SharePoint 2010 publishing web site it looks like this :-

Note the GroupGuid site column.

This is what the Relationshiplist list looked like after I upgraded the site from MOSS 2007 to SharePoint 2010 :-

Note the GroupGuid sitecolumn is not there !

This was the column that RemoveAllExceptOneListItem uses to do a SPQuery on !! Hence the Error message.

The solution :-

Use Chris O'Brien's tool to export the RelationshipList list from a site which works (To do this add an appSettings key in the application config file named 'ListsNotForExport' and specify a comma-separated list of the lists you wish to hide). Then import it into the site which does not work. But do not set "retain GUID". Your site will now work !