Not sure I completely understand. From what I read, it sounds like cPanel was installed on the server already and you (thought) you deleted it before installing Plesk. From reading the error messages and file paths, however, it sounds like it was not completely removed - which probably cause all of the issues mentioned in this ticket.
Regardless of whether you wish to proceed with Plesk 11 or cPanel as your control panel solution, I would _really_ recommend that you totally wipe the server and start over. It's very likely that there are remnants of one or both of the control panel solutions still remaining.