E: Package proftpd has no installation candidate

[Jimmy Tak <f.l.tak@leden.snt.utwente.nl>]

I'm sure it has been asked before, but I couldn't find it. When I try to 
install proftpd I get the following error:

Reading Package Lists... Done
Building Dependency Tree... Done
Package proftpd has no available version, but exists in the database.
This typically means that the package was mentioned in a dependency and
never uploaded, has been obsoleted or is not available with the contents
of sources.list
E: Package proftpd has no installation candidate

I can't find it with apt-cache search either. I've tried several sources 
and I did my apt-get update's. Whats wrong here?

Thanks in advance,
Jimmy Tak