Session Drummer Latency Mystery

Hi,
 
The strangest thing happened today. I opened a previous project (mixture of live instruments and VST's), and decided to try inserting a Session Drummer instance using the "MIDI Source and All Synth Outputs" option in the soft synth options. It plays the original drum track great, however there is now a latency issue for all the other VST's including Session Drummer. It all plays back fine, but there's a serious delay if you want to record anything. My latency settings are ideal, and it ONLY happens in this particular project. Is there some sort of funky thing that I'm missing?

On that particular project, look for other sound enhancing plug-ins, some of them cause considerable latency, whenever I use perfect space, I turn that off, exit & save.

Also on your tool bar, the tools that show mute, there is a PDC radio button, enable that will take care of latency as well.

Those plugins fall in a class of effects that require a look-ahead buffer to work properly. That buffer means that everything must be delayed a bit in order to stay in sync.