The first time this happened, it took me hours to discover what causes this. I tried the Print Center repair utility I found at VersionTracker, but it didn't help. In the Apple discussions area, someone mentioned that after changing the rights for /tmp (to writable for everyone), printing worked again. That did the trick for me, too.
Today I checked a second (correctly printing) system and it appears that /tmp on that system is a symbolic link to /private/tmp. So I restored that symbolic link on the malfunctioning system and printing now works again. Apparently I had used an installer or something that had overwritten the original symbolic link.
I hope this saves other people some time when solving printing problems.

