If you want to see the picture at full size you can right-click on the image, choose copy, then open Paint and paste into it.
 
Many hours on sessions with big sample libraries may be a memory issue. The great thing about 64-bit systems is you can load a zillion libraries into RAM, and 64 GB sure seems like it would be plenty for just about anything, but multi-gigabyte samples add up if they're left in memory even if you're not using them. Kontakt has a purge function to help with this, not sure about other samplers. Note that even streaming from disk uses up quite a bit of memory because the sampler has to store all the note attacks in RAM.
 
Might be worth getting into a workflow for a week or two where after two hours you save, re-boot to clear out the RAM, then re-open the project and see if the problem still occurs.

Wookiee
I would highly recommend you reporting this with the emphasis on it being time related issue. I have noticed some oddities with the paste function when I have spent time MIDI editing. i.e. miss pasting even when using the option to paste special or the keyboard short-cut ctrl-alt-V, telling where to paste to have it paste starting on a different track.

I certainly wouldn't bother reporting it until better steps can be obtained. Without even slightly better steps to repro I suspect QA would probably skip this and move onto another issue more easily reproduced (better use of their time). It will be like searching for a needle in a haystack. Right now it's far too easy to assume it's an environmental issue (whether that's true or not remains to be seen, it's anybodies guess). If it's a screen refresh issue you might try updating your display drivers (for what it's worth).

Yes,  this does happen.  I have experienced it many times, for many years.   It is a memory and buffer issue.  your edit history and other things become overwhelming.  So you save and exit (try emptying your Picture Cashe folder on occasion also, that solves many of these issues!).  When you reload the project it will be good for again for a decent amount of time (if emptying the Picture Cashe folder fixes things it will be good for a long time.)
 
Panu's program "Duckbar" will do this for you.  Dload this program and look under "Tasks"
 
http://www.sonarmods.com/forum/index.php      
 
Plus it will make your Sonar GUI look really cool if you so desire.
 
A more powerful computer with more memory will help also. I think I need to upgrade mine.

Jimbo 88
A more powerful computer with more memory will help also. I think I need to upgrade mine.

But the OP has an i7 and 64 GB of RAM, not quite sure where he'd go from there. I don't know enough about computers to comment on this in depth, but I've heard of programs not releasing data from RAM and just continuing to fill up the RAM until eventually, there's not enough room left for basic operations (like storing data in RAM for pastes), and I've also heard about "memory leakage." Maybe someone with more computer savvy could give more details.

It could just as easily be a drivers issue (most likely audio interface). I would update all drivers and firmware everywhere and run windows update several times. Update motherboard bios and chipset drivers.
 
Right now impossible to tell.
 
Memory leakage could be any buggy app, but that could be down to any app or any drivers. Or it could be caused by something like antivirus locking the files of an app turning it into a buggy app. The best way to tell if that's happening is to download a copy of process explorer (taskman replacement) and just keep monitoring the graph, if you start getting cores filling up to 100% you are in trouble and you can locate the process effected (note I see process effected it could be some other process that's causing it). You could also monitor your memory/IO/GPU if you like on the summary graph
 
We however don't really know if it's even a memory leak yet.
 
In fact I'm experiencing an issue with this myself (unfortunately with no steps to repro) with the Native Instruments hardware service and control surfaces maxing out cores in Sonar. Looks like a NI issue but hard to tell right now so not pointing fingers..

BTW the end result is it crashes Sonar but it's hard to tell whether it's VS700 controller, the NI service or NI drivers right now, or indeed Sonar core code. To the layman it would look like Sonar crashing but there's no way to point the finger right now of the cause without more detailed research.

All good comments.   As noted I have a pretty good computer, lots of ram, a good audio card with latest driver.   As far as I know there's nothing odd about my workflow, but who knows?   Sometimes things I do, and post about, get greeted here with "oh I never do it that way..."
 

Maybe someone can improve my workflow: I spend endless hours taking a single track, derived from a printed score, and breaking it into many tracks in order to make an instrument with many different articulations: staccato, accent, legato, spi-ccato, quiet, loud, sustained, crescendo, diminuendo.   So lots of selecting small units, cutting from the source track, and pasting into the destination track.
 
 

williamcopper
Maybe someone can improve my workflow: I spend endless hours taking a single track, derived from a printed score, and breaking it into many tracks in order to make an instrument with many different articulations: staccato, accent, legato, spi-ccato, quiet, loud, sustained, crescendo, diminuendo.   So lots of selecting small units, cutting from the source track, and pasting into the destination track.

 
I haven't read most of the above posts, so this might have already been suggested, but I think you just need to select those note events in the PRV and click one of track headers in the Track view (to move focus to the view) and then hit Num 8 or Num 2 to move those notes to the previous or next track. I actually never move notes or clips using Ctrl+X and Ctrl+V or Paste Special (Ctrl+Alt+V), which I find not very efficient. I use either Nudge or (Shift-)dragging. Note that nudging notes in Take lanes can cause a serious problem (confirmed as a bug), so don't do it in Take lanes. 

Anderton

Jimbo 88
A more powerful computer with more memory will help also. I think I need to upgrade mine.

But the OP has an i7 and 64 GB of RAM, not quite sure where he'd go from there.

The acuity of your responses amaze me every time Craig. Now and then I get to laugh out loud as well:)