You cannot mount or unmount folders in the Media Manager, or the folders are empty.
The Media Manager is using several database files, that might need a re-indexing
To force a re-indexing of the Quickmount files of a specific folder, select the folder in the Media Manager and click on Refresh whole holding CTRL key.
Pyramix is also using a meta database, storing informations on all media files.
Go in All Settings/Application/General and untick the box Keep Media Manager History, then restart Pyramix.
This will flush the complete database.
If it is already turned off, go in All Settings/Application/Location and click on Browse next to Default database location and set a new database location.
Then restart Pyramix.
you may also close Pyramix and go to C:\Users\username\Appdata\Roaming\MergingTechnologies\Pyramix\Database: delete all files .