JonD
Aha!  Drives nearing full capacity can exhibit all manner of strange behavior.   I'd fully expect dropouts, etc. with a nearly full drive in a recording rig.

Really? That's interesting. Luckily it's nearly time I upgraded my PC so this problem may just go away by itself, if I can't find another fix first. But there definitely seems to be something wrong with the graphics or USB at a minimum.

A slow (or failing) hard drive can definitely exhibit all kinds of weird problems or crashes. I had a system with a failing drive that was throwing various dropouts and crashes in SONAR. I used it to advantage to make SONAR's handling of these situations more robust :)
Try clearing your picture cache and freeing up some space. If disabling all fx still causes issues then the drive seems to be a likely candidate esp if the problem occurs in audio only projects. Try isolating it by also removing soft synths one by one.

For the benefit of the curious and anybody who finds this in a search, I found the culprit. I use a program called f.lux (or 'Flux') which changes the screen brightness and colour cast on an evening to create a less harsh viewing environment after sunset. Unfortunately the routine it uses to change the colour seems to be momentarily intensive, perhaps because it requires the graphics card driver to take some sort of action. Whether it's f.lux or the driver at fault is hard to tell, but I have the latest drivers so there's not much I can do on that front. Exiting flux gives me smooth audio playback - and half-blinds me, since I'm used to the duller screen, but that's the price I'll have to pay.

Thanks for posting your solution back on this Dan.  One more thing to add to the troubleshooting list.
 
Glen

Kylotan
For the benefit of the curious and anybody who finds this in a search, I found the culprit. I use a program called (or 'Flux') which changes the screen brightness and colour cast on an evening to create a less harsh viewing environment after sunset. Unfortunately the routine it uses to change the colour seems to be momentarily intensive, perhaps because it requires the graphics card driver to take some sort of action. Whether it's f.lux or the driver at fault is hard to tell, but I have the latest drivers so there's not much I can do on that front. Exiting flux gives me smooth audio playback - and half-blinds me, since I'm used to the duller screen, but that's the price I'll have to pay.

Can't you just turn down the screen brightness in Control Panel/Display?

Flux is automatic, gradual, and adjusts the colour temperature (which is subtly different from just adjusting brightness)

Ah you just tried to help me in another thread, I hope I might return the favour!

I still use a 14 year old 2496 at 44100/128 using M-Audio Delta Control Panel 6.0.8 on Win 8.164 X3, Komplete Ultimate and a load of others. i7 4790@4.6 16GB RAM, SSD's....

In Sonar I have timing masters both set to the Delta AP SPDIF, 24bit depth, Mixing latency Buffer in Queue=2, Buffer Size = 2.9msec. I use WDM and have no dropout or latency issues at all.

I have the same tiny latency in every program I use, including just standalone Absynth or Kontakts, SD, whatever. Also in Ableton Live.

BUT

When I use a heavy Convolution Reverb plug in, say Perfect Space with a high quality WAV.....Then I have a huge problem if recording, not mixing, but most of the time, using almost everything you do Absynth, SD, and so on things are fine and at 2.9ms almost realtime. I rarely need to freeze tracks..

Is the 2496 card failing? I have also found on occasion I have needed to remove, dust and reseat the card over tha last 14 years :)

Cheers

What is the purpose of the picture cache and what happens when you delete the files in this folder?
 
TNX

Oh too late, It was f.lux! LOL.

Great program that!

TremoJem
What is the purpose of the picture cache and what happens when you delete the files in this folder?
 
TNX

The picture cache is the "wave forms" you see in the Track View. To speed up loading projects, these are saved so that they do not need to be recreated, but they can accumulate over time. Deleting them simply forces SONAR to recreate them as audio files are loaded (and will take a little longer to load by doing so).