If you are experiencing missing folders in the RadEditor Image Manager in DNN please follow these simple steps to fix the issue:
The problem is often caused by upper case letters in the folder names. The following script sets all folder names to lower case in DNN's folders table which will resolve the issue.
SET [FolderPath] = LOWER([FolderPath])
Then go to Host > host settings and click Restart Application
AND if that wasn't enough, and the image manager is still empty, keep reading.
I have seen two portals where, in the File Manager, the folder permissions were set to deny "Open Files in Folder" and "Browse Files in Folder" for all folders. I cleared the red dash in the check box on the folders and now the image manager showed folders and files again.
I am not sure what process has changed the permissions to deny, but I am confident that it was not me or any other person.
Good luck to you. In my Internet searches I saw quite a few people having trouble with the image manager being empty.