Weird timing issues with simple MIDI file...

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.

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.

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?

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.