I'll create a MIDI track using either the piano roll or staff view.  Typically if the measures repeat later on, I'll just copy/paste.

When I "freeze" my VSTi, many times the copied measures won't transfer over and I'm left with just ONLY the original MIDI measures transferred to the frozen audio track... and obviously the final frozen track much shorter in length than what they should be (with my copy/paste measures not included).
 
My work around has to been to "bounce to tracks" and then disconnect my synth in the "synth rack". 
 
With my older setup, I have to freeze some heavy hitters, or else the CPU goes out the window.
 
Obviously a bug on an older version I don't expect a fix to.  Anyone else experience this or have an idea?

I too have found that copy /paste is a bit buggy. 
 
My solution, which I have no clue to why it works, is to always use the "split" function. 
This seems to have solved the weird behavior for me. 
 
I take the measure(s) I wish to copy and I split the track(s) at the beginning and end of the part.  Then I highlight and use the copy paste function. If I'm inserting it I will split the location and drag the track right to make room and copy using the "replace" option. "Slide over to make room" is always hit or miss for me. Haven't had any issue since adopting this procedure. 
I use this method for both Midi and audio tracks. 

thanks, I'll try that and report back.

Naw...it didn't work and I tried variations of splitting, streaching, etc.  However, when UNfreezing, it would now consistantly cause a fatal error in Sonar, the window would pop up  "Should Sonar attempt to save....blah blah..."  then Sonar would zzzzzzzzzziiiiiipt!.  But at least the computer continued to run.
 
One suspicion is my Toontrack Superior Drummer.  I've had MINOR issues with it before, shuttling clips around and such, and it would crash the program when bouncing or freezing.  However in my latest session where this is happening, I am able to freeze the Toontrack MIDI tracks.... but get this NOT an Easy Drummer MIDI track in the same session (using the EZX electronic).
 
Oh well... X3 is on the horizon with a new power plant to run it...   S/B history soon...hopefully

not that it matters... my Toontrack Easy Drummer in this case isn't freezing properly...as are my two DimPro tracks...  but ONLY the DimPro crashes Sonar when I try to UNfreeze.   The Toontrack Easy will at least UNfreeze...but the Superior will be just fine either way...  gotta love it! ;-)

Yep, looks like your old system is not up to it any more.. Good news is that computers are always getting more powerful but at the same price point. 
The Layla might have to go too as I think it's hard to find anything to run them in the new systems. 
I only have a basic computer by todays' standards - 2 cores/ 2.6 Mz and 4 Gigs of Ram. But it never freezes or screws up on me.