I'm leaning towards a database issue here...  basically because I doubt you've got localized content in your site(s)?

1. You have a case mis-match in your foldernames.
There's a known issue that if you have, a vs A.
You'll see an error in the Event Viewer of your site with a stack trace similar to this:

DotNetNuke.HtmlEditor.TelerikEditorProvider.FileManagerException: Unable to complete operation. An unknown error occurred. Portal Root ---> System.ArgumentException: An item with the same key has already been added. at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value) at DotNetNuke.HtmlEditor.TelerikEditorProvider.FileSystemValidation.get_UserFolders() at DotNetNuke.HtmlEditor.TelerikEditorProvider.FileSystemValidation.GetUserFolder(String path) at DotNetNuke.HtmlEditor.TelerikEditorProvider.PortalContentProvider.AddChildDirectoriesToList(Dir ectoryItem[]& radDirectories, Boolean recursive, Boolean loadFiles) at DotNetNuke.HtmlEditor.TelerikEditorProvider.PortalContentProvider.GetDirectoryItemWithDNNPermis sions(String path, Boolean loadFiles) at DotNetNuke.HtmlEditor.TelerikEditorProvider.PortalContentProvider.ResolveRootDirectoryAsTree(St ring path)

2. You have bad data in either the Folders or Files tables in your Database
You have fixed paths for folder paths that matched your staging environment and these need to but did not change when the application is moved into your Production environment.

In your case the folder and/or file paths for your data may be incorrect in the database and you will need to change them.