It's been a long time since I used 3.006 but more likely than not your database became corrupt. The quick and easy fix would be to change the songs backup.mdb file in the database folder to songs.mdb, or the slightly longer but maybe easier fix would be to rebuild the database.
First thing I would try to get Hoster running again would be to try and do a restore to a point before you uninstalled it, If that works rebuild your database.
I haven't seen that error mssage in a long time but if memory seves correctly I think it's telling you that you put in an invalid registration number. If you typed it in that is probably the case, it's very easy to type incorrectly. It's best if you can copy and paste from your original email.
If none of this works I'd suggest
submitting a ticket to support
Sam