Actually, I think its more likely your problem is that the OS Package Manager thinks you still have the Package Manager's repo fp-compiler installed. I guess you don't have synaptic package manager installed ? Its a far more powerfull tool than the things they ship called "software Install" and the like. Either way, maybe its time for some command line work ?
At a terminal, try -
dpkg -l | grep fp <enter>
The the '|' symbol, a pipe, its usually to the right of keyboard, shown as a vertical line, its not an alpha numeric. The command firstly lists all installed packages and that is piped to the grep that filters out all except a line that has fp somewhere in it. So, there will be lots of hits ! Look to see if what you interested in is listed. If it is, it must be removed with package manager, don't be tempted to remove the files, the package manager will still believe they are there !
Davo