Umbraco admin tree not showing up

If
1) Umbraco admin tree is not showing up and
2) is determined not to be a problem with the trees.config file and
3) Clicking on any of the navigation elements gives you
         Request error: The URL returned a 404 (not found):
         views/propertyeditors/undefined/undefined.html

Check permissions on the website folder for iis users.
Easy way is to give machinename\users full security access on the folder.