If you can open a support ticket and send me the project files and a backup of the database I will be able to examine the issue in more detail and better advise you on the cause.
This is most probably caused by some error occurred during the upgrade.
If you still have the 4.0 project you can send it too to test upgrading it at our end to see if the same complications will occur.
The proper upgrade path is 4.0->4.1.1339->4.1.1395/1501/1574 ->4.2.1650->4.3.1885->4.4.2117. After each upgrade run the project and log to the backend of the site to perform the database upgrade.
All the best,
the Telerik team
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