[Solved] Sonar Platinum - Midi Latency with only one project.

Normally, unexpected latency in a particular project would be due to some pluging using a lookahead buffer that induces automatic plugin delay compensation, but not if the latency is more than a small fraction of a second. Latency that high would make me suspect a driver probelm... but not if it's only one project. 
 
Are you sure the latency is really more than a second? If you hit the PDC (Override) or FX Bypass buttons in the Mix module, does it help?
 
Also, it's a little confusing that you refer to the Alesis kit as a 'virtual instrument'. The Alesis kit is a MIDI controller with combined hardware sound module and MIDI interface that I gather you're using only send MIDI to EZdrummer which is the virtual instrument. Are you connecting the Alesis MIDI output by the USB port or by the DIN connector to another interface?

Cool. Glad to help. Ideally you should try to avoid using Mastering FX (e.g. Convolution Reverbs, Cakewalk's Linear Phase EQ and Multiband Compressor) while still tracking. As a drummer, you're also likely to be using Transient Shaper which also induces PDC.
 
The PDC button in the Mix module can be used to temporarily override delay compensation on input monitored audio tracks (including synth tracks) to allow tracking a new part without the added latency, so long as the PDC-inducing plugin isn't on the track you're recording.
 
Check the Ref. Guide for more info on PDC.

Try increasing the "Prepare Using nnn Millisecond Buffers" value in Preferences > MIDI > Playback and Recording from 250 to 500 or 750.