Hey I just reinstalled X1 Essentials on my PC.  After tinkering with the audio settings I finally got some sound out of a project I had previously work on on another PC. However, some of the MIDI notes are sounding and some are not.  

For example if the piano roll has a repeating riff of 16ths going a-a-b-c let's say, the program will randomly cut some notes out.  Like it might play a-a-?-c, a-?-?-c    etc....

Does anyone have an answer?!?!?! 

What soft synth are you using? Polyphony settings could cause "note stealing" problems.

It seems not to matter which synth I use...TTS1, SI..

Oh... well... we could do with more information about your setup then please.

AMD FX-6100 6-Core 3.3 GHz, ASUS M5A97 AM3+, Kingston 4GB DDR3 @ 1600MHz, MSi R7750 OC 1GB GDDR5

Still building my setup so I'm using onboard sound for now and no MIDI In's

Okay, I think you will find that most peeps here will say to ditch the onboard soundcard and buy some kind of proper audio interface, either internal or external.

I realize that but I had this working on my crappy 8 year old Toshiba Laptop...suppose I'll keep attempting to tweak things.  Thanks for the help anyhow.

I bought a brand new i7 laptop with 16gb RAM, etc. etc. and it just would not function with the onboard soundcard, no matter what I did with the settings. As soon as I got my QUAD-CAPTURE, all worked fine.

If you are still building your system, then a decent audio interface should be your next purchase...

Double your MIDI-preparation buffer "MIDI buffers ... Prepare using xx ms buffers"
That's most common reason for randomly skipped MIDI-notes starting from SONAR 8.

I must have written this answer a hundred times during the past year.

ditto on the soundcard issue. 

I have an older Dell and no amount of fiddling with the settings has ever allowed me to use the onboard sound card.  It simply refuses to play nice with Sonar products. It plays MP3's and the other programs just fine. Sonar... nothing... 

However, I plug in my Focusrite Saffire and there is no problem playing the biggest Sonar projects. 

Regardless of what it did on a different computer does not matter.  The important thing is what it does on the new one, and I suspect you will need to get a decent USB external interface which uses ASIO drivers. Once you do that the performance will be outstanding.