Symptoms:
When attempting to use IMAGE/DOCUMENT/MEDIA MANAGER within a module, the file selection window is grayed out or blank.

Resolution:
This may be due to one of several issues:

1. The website user (the application pool identity, which in our case is the "IWPD user") may not have permissions to the applicable folder.
   • Please contact our support team to have us verify if the website user permissions are set appropriately
2. You may be missing appropriate references in the DNN database's tables for FolderPermissions that allow access to the folder you're trying to access.  This issue is caused by bad permissions in DNN’s database for the “Administrators Role” or roleID 0. (This may vary depending on the DNN instance, role 0 is the common role for the RoleName, see that RoleID 0 is assigned to PortalID 0, so if you’re working with multiple portals, this may be a bit different.  Just keep all this in mind.  In short, when you cannot upload to a folder in DNN and you've confirmed the server-side permissions for the site user (IWPD User)are correct, this leaves an issue with the DNN instance, specifically with entries for the DNN user in the following tables: dbo.Folders and dbo.FolderPermission. 
   • Attached is a walk through of checking the applicable entries in the DNN database, and correcting this issue.
3. The physical folder names may be out of sync with the folder names within the Folders table of the DNN database, including case-sensitivity. If the physical folder name under /httpdocs/portals/PORTAL#/ is "Images", while the associated table entries in the database are using "images", the DNN Admin/Host File Media Manager isn't able to properly update the Folder table.To resolve this, you will need to update EVERY relevant table entry for the portal,  either manually  or using a SQL script. Alternatively, you can also remove all entries for the effected portal from the Folders table, and then run a recrusive file sync from the DNN Admin File Media Manager.

• We strongly recommend you request a full backup of your DNN site's database before making changes in it.
• Or, you may wish to contact our support team, who will also investigate and, if possible, resolve this DNN database issue as a courtesy.