zzeliminator, I'm like Roy, we are not aware of any reason why 12,000 is a magic number. No one else has reported this, so it "appears" to be something related to your computer.
I would recommend you go to
http://www.mtu.com/upgrades/hoster.htm and download and install version 5.03. We did a lot of improvements to the Songs and Singers Databases. This alone might solve your problem.
When you run 5.03, it will rebuild both your Songs.mdb and Singers.mdb Databases adding new fields and creating indices for some fields. This will totally rebuild your Songs.mdb. If it stops at 12,000 you need to contact MTUSUPPORT using the Help Ticket (
http://www.mtu.com/support/customer-...htm#HelpTicket ) and explain the problem to him. He may need to call you and remotely enter your computer (with you present and watching) to diagnose what is causing this limit.
If you want to try manually rebuilding the Songs.mdb in version 5.03, click the menu bar "Import Songs" command, then the "Build Database" button (top of dialog), then in the "Indexed Folders" list (this named button will be green at the top right of center) at the bottom left and make sure all your folders are added there. Click one and click the "Refresh Folder" button. It should indicate progress while the KMH files in that folder are replaced in the Songs.mdb. Do this for each folder.