The two MIDI humanizing plugins that I have worked fine in Sonar X3P. I applied the same tweaks to Platinum's TTSSEQ.ini file that I had in X3, and I'm getting loads of dropped notes on whatever track I use the humanizer on. (I'm using it primarily on drums VSTs like Steven Slate 4, AD2 and SD2 and they all do the same thing with the two humanizers) One of the humanizing plugins is the Cakewalk Quantize midi plugin. The other is one I bought here: http://www.midi-plugins.de/
 
They both present the same issue.
 
I tried to set the playback buffer to > 250 ms in Preferences > Midi > Playback and Recording, but that made no difference. I don't really like the Humanize CAL that comes with Sonar as I don't think it adds enough timing variation at all. I could realistically go through by hand and manually alter the midi file. But I want to try to get Sonar to work correctly with the paid MFX plugin....since I DID pay for it, afterall, and it worked fine in X3.
 
I added the MfxLookAhead line to TTSSEQ.ini, but that also made no difference.
 
Any clues or help would be greatly appreciated.

did you try increasing prefs-->MIDI-->Playback & Recording--->playback? Might try 500ms, 750ms, or even 1000ms.

Yup tried all that jazz.

What's interesting is that last night when I went searching for the TTSSEQ file in %AppData%/Cakewalk, it wasn't there. It only showed up this morning when I loaded Sonar after booting up my machine. I wonder if Sonar is even reading that file. That's where the MFXLookAhead option is located.

After further experimenting, I found that if I set the MIDI buffer in the preferences to something really high like 1500 ms that this issue is resolved. (Note: this problem only occurs when using humanizer plugins)  I'm not sure what changed between X3 and Platinum, but there ya go. This does present the issue of the first note of a loop being cut off at random times, but I'll manage.

Thanks for that Vern.  I'm a big fan of "Frank's Midi Plugins". although I haven't used the Humanizer in a while.