I can't release a player?

Atlanta waives Cedric Bozeman.
Now I forgot the website where I got my roster patch (NBALLO) from, but when I try to release him I get this...

I done some DBF editing to move him to the Free Agent Pool, but it didn't work. Any suggestions on what else to do?

Check is ISHISTORIC attribute, it may be set to True. It should be set to False.

The ISHISTORIC attribute is set to false.
I am also getting this for other players that was recently released.

I'd say there's a problem somewhere in the dbfs, though I can't think what since my previous suggestion is the only one that comes to mind. You might want to contact the person who made the roster and ask them to check it out.