Jos,
In my situation my printer has an internal Jet Direct card. So, I have the printer defined in server-manager as remote with the IP address that I assigned to the printer. I didn't test this with printers off of the LPT ports. You could try the same thing I did one printer at a time. Remove one of the printers, and then re-add it with the exact same name. That way you shouldn't have to change anything on your clients. See if you can manage it from in Windows clients. If that doesn't work, then try a reboot to see if you can manage the newly re-created printer. I don't remember if I had to reboot my server or not, but it shouldn't hurt anything that I can think of.
JB