Mine sitecore upgrade installation from 6.4 to 6.6. The important part in the error message was the error location
Sitecore.Shell.Applications.Layouts.DeviceEditor
. Running a compare between a standard sitecore 6.6 installation and my local installation I discovered that the file sitecore\shell\applications\layout\deviceeditor.xml was outdated. Replacing the file with the correct version resolved the problem.