Comment 15 for bug 55283

Geoff Jacobsen has the same problem in bug #36532.

He was able to solve the issue by reinstalling gs-esp with following commands:

$ sudo dpkg --purge --force-all gs-esp
$ sudo apt-get install gs-esp

Then you can add the comment in mime.convs again:
#application/vnd.cups-postscript application/vnd.cups-raster 100 pstoraster

You only need gs-esp, you can safely remove gs-afpl and gs-gpl with following command:
$ sudo apt-get --purge remove gs-afpl gs-gpl