I also noticed I got error 199-9999 when launching the USB Launcher GX forwarder (installed to NAND), even though I confirmed Tiramsu was running. I removed the WiiU formatted drive and tested again and it then worked. I then deleted and reinstalled it on USB, and it worked. Moved it to Wii U NAND with Memory Manager and it didn't work again, unless I removed the USB drive again.
What I've now done is copy it to the Wii U USB drive, so if it's in, it launches from the USB drive, and if it's out it launches from the NAND, so appears to be a bug somewhere launching it from NAND when the Wii U USB is connected.