Hi, 
Longtime user with very fast audio only computer. Running latest Platinum version of Sonar.
Simply load a commercially bought MIDI file of a pop song as I have for 25 years. Playback is fine with the onboard cheesy synth player, but when I loaded Dimension Pro Horns to replace the cheap synth sound, the horns were delayed by a second or less. Yes, I could go into piano roll and lasso the lates notes and move them, but I don't know why this is happening. Same things with trying to assigned Addictive Drums 2, only editing the timing of those notes would be a nightmare.
I looked at my Presonus Firebox latency settings, Asio, all looks well.
Any ideas?
Thank you.

Is playback OK using TTS-1 in SONAR?

To save time, make sure no MIDI output devices are selected in SONAR Preferences, then open the MIDI file. SONAR will automatically set up TTS-1 for the MIDI file.

what is your midi buffer set at ? I believe 500 is what you should be aiming for.
could be related to soundcard (latency). typically its cracks/glitches in midi it is a buffer issue.
but it still might be worth a shot if Steve's idea doesn't produce positive results.

Yes, thanks, about 500 is what I have.
 
I'm gonna try TTS now, but in the mean time, the onboard synth showing is, Microsoft GS Wavetable Synth, which plays back the MIDI file fine. But as soon as I assign Dimension Pro horns, they are coming in late.
 
I guess when I report back on the TTS working or not working, that will tell you something?

OK, I disabled the Microsoft GS Wavetable Synth (which had played the MIDI file fine), and when I opened the MIDI file, assigned the TTS.
TTS played it back fine too, but, this time when I assigned a DP Horn, the timing of the horns were NOT thrown off. Don't know why, but now I can go ahead and assign other instruments.
Thanks for your help all.

Jerrycast
, but when I loaded Dimension Pro Horns to replace the cheap synth sound, the horns were delayed by a second or less.

What is the exact name of Dimension Pro patch you are using?  Does the same problem occur with a patch with a low attack time - like a piano).  Sometimes I am using a patch with a high attack time.  Therefore, the note triggers (on the beat), however, the crescendo of the sound actually occurs late because of the high attack time.  In this case, rather than moving all notes slightly to the left, I use the time offset function in the MIDI track inspector (just above the patch browser) to trigger the note just before the beat marker.  Mind you, a second seems like a long attack time, even for horns.

Thanks promidi.
Interesting, I'll have to try that. Although, I didn't mean that the Attack Time was one second, I meant that there was a very short delay (milliseconds) before the horns sounded where they should, so I described the amount of time as one second or less.
Even with Cakewalk from 1992 I've never had any attack time problems with any synths (all hardware back then), so that's why I didn't think it was the attack times.