Another point that might be good to throw in here is advice from the Melodyne (Editor) manual below. I actually do exit and reopen programs (in general) to release RAM out of habit, and this "may" be a reason for bugs seen in "long sessions." It is actually good advice from an "objective DAW observer."
 
"Restart your DAW at regular intervals: Many DAWs have a tendency, the longer they run, to
monopolize more and more RAM, which they fail to give back to the operating system in the correct
way. This is something you will notice typically from the fact that the RAM display (in the Task Manager under Windows or the Activity Monitor on the Mac) will show less and less free RAM
available even though you haven’t performed any additional editing in Melodyne or added new
sampler instruments. Restarting your DAW at regular intervals, you will find, works wonders in such
cases. As a rule of thumb, we recommend the following: each time you leave off editing one (fairly
long) track with Melodyne, before you begin work on the next, you should save the song and restart
your DAW. Only then should you perform the next transfer and resume editing.
 
© Celemony Software GmbH 2013 • Last updated on 07.10.2013 • Online Manual • www.celemony.com 39"
 
 

I guess you would get performance monitor out and check to see if you are running any leaky software.
I seem to be able to go on all day without issues... touch wood.

 
At the very least turn the computer off every night and start afresh the next day.
 
My daughter was complaining the other day that her laptop was slow.  I asked her when was the last time she'd shut it down.  Several weeks ago.  Firefox was up to hundreds a megs (it's got a huge leak) and she had I don't know how many documents open (she's at university) and a bunch of other stuff.  It was horrible.  The process list was a mile long.
 
 

Yup it also saves the electricity bill.

For the history books ... and anyone finding this thread in the distant future ...
 
All of this was an issue between NI Kontakt 5 and Roland Octa-Capture audio interface ... no system problem, nothing to do with OC, no Sonar problem (although Sonar suffered from it and hence was the unfortunate prime suspect) ...
 
It took more than a year to track down and find the root of the problem... and more than 2 years to see an update in Kontakt 5 which addresses problems with Roland interfaces (more here if interested)