Trouble filing IFR to Canadian Airports

I've made this flight many times before and never encountered this
before. I filed from my home airport (MGY) to PT(which is an NDB) to
CYKZ using DUATS. Everything went fine. When I called for my
clearance, they didn't have anything on me. So I departed VFR, and
tried calling again. Still no luck. They tried manually entering my
flight, but then said they had trouble entering my Canadian waypoint
and destination so I better call Flight Service. I filed with FSS and
called ATC again, but still ATC had nothing for me. I called FSS
again. Now he says his computer would not take CYKZ or PT, and the
only way he could do this is if I provided the lat/lon for these
places. After shuffling through a lot of mess, I found the co-
ordinates for CYKZ and read the numbers. I said forget the enroute
waypoint; I'll go direct. After nearly one hour after departure I
finally got my clearance. It was good time too because we were in IMC
not too long after that.

I was totally puzzled by this. Since when did Canadian airports and
navaids disappear from US computers?