Erratic timing with MIDI

[Olixka]

MIDI recording / playback in PT M-powered 7.3 is very erratic so I gave up trying to do music with it, and tried just to implement the MIDI click ... on record+playback, in an otherwise empty session.

I'm using PT's inbuilt 'Click' instrument and there are no other MIDI devices connected.

So there should be virtually no demands on the CPU of my 2.6 GHz Windows PC. Delta 66 soundcard. (Audio recording appears to work well.)

The metronome plays much too slowly, and also extremely erratically ...
"click (long pause) click-click-click (short pause) click click (very long
pause) click" etc etc ... completely useless for timekeeping.

It seems to me that the counter is advancing erratically as well. The tiny decimals in the transport window don't advance smoothly.

I've followed all the procedures in the pdf manual and on the instructional
DVD to the best of my ability. Is there some blindingly simple thing I'm overlooking? Could it be related to the dual processor and if so, how do I tackle that? FWIW recording on my old Cakewalk software on the same PC has none of the above problems.

Any help much appreciated.