I recently loaded some old projects into sonar. I decided to redo the midi drums with my Roland td15, but there was an unreasonable amount of latency. 
I've never had a latency issue with my current setup so that was strange. I got around this by loading the some guide tracks into a new project, recording the drums then importing the performance back into the original project. I then tried to add some midi keyboard and same thing...big time latency.
 This project was recorded a few years ago using sonar x3 with a different computer. I'm wondering if there is a setting somewhere I may have missed.  I also checked with some other projects from the same sessions with the same result. So it seems I cannot insert a synth track into an old project without latency issues.  Anyone have any ideas?

Usually this is caused by Plug-in Delay Compensation added by SONAR to adjust for plug-ins with look ahead buffers. Try typing "E" to disable all effects. If the latency goes away, this is the clue some plug-in(s) are the source of your problem.

Yes that was it. Brilliant! Thanks Scook