I’ve run into this issue before. Ultimately it boils down to a database corruption but don’t get too worried. It’s recoverable. 
Here’s what I did.
Process 1: Data Security aka backup the databases.
Close DAZ Studio.
Stop the DAZ Content Management Service
Backup your databases folder. (Just copy the whole folder to a new location).
Restart the DAZ Content Management Service.
Process 2: Exporting User Data
Start DAZ Studio.
On the Content tab go to the context menu at the top corner and select Content DB Maintenance.
Check the next to last checkbox “Export User Data”.
Wait patiently. This process can take a LONG time. (it took my system almost 2 hours) and DAZ Studio can appear as if it is “not responding”. Just leave it alone until it finishes.
Exit DAZ Studio
Process 3: Scary time!
Make sure DAZ Studio isn’t running.
Stop the DAZ Content Management Service
Delete the contents of the databases folder. @_@ Yes, that’s right. Nuke it from orbit. kaput! Delete, gone. ^_^
Start the DAZ Content Management Service. (You’ll note that it recreates several files in the databases folder).
Start DAZ Studio.
It will prompt you to import metadata and you’ll note it will also mention “User Files” in the list. Make sure those are checked.
Let the import process run (it’ll run about as long as it took the export to run, maybe a little longer).
Breathe a sigh of relief as you note that almost everything appears normal.
Scan Known Directories for Files.
Breathe a sigh of frustration as you realize that, yes, some stuff didn’t make it. This is the stuff where the corruption was (for me it was an entire tree of stuff).
Recategorize and go.
Process 4:
Make regular backups of your DAZ CMS databases.