Plexwriter PX-S2410TU burning problem

I bought a Plexwriter PX-S2410TU CD burner recently. Burning files on a blank CD-R is no problem, but when I want to add files or data to a CD that has already data on it, I get an error message saying “CD is not empty”.
Anyone any idea how I can solve this problem? Thanks

You need to create a “multisession” disk when you do the first burn. You can then add more ‘sessions’ if there is still enough space left. The procedure for this depends on the software involved. PlexTools Professional does not offer functionality for adding additional sessions, but lets you at least start at multisession disk (“leave disk open”).