Whether you believe it or not, your extra info is invaluable - particularly since you highlight which video card you are using - this all makes a difference to everyone trying to interpret your anecdotal testimony.
Unfortunately nVidia appears to have abandoned those of us with older PCs and video cards. I have a 2008 Gateway PC with i7 processor, 6 GB RAM and GeForce GTS 250 video card. I haven't been able to use GPU rendering for more than two years since I upgraded video drivers from an earlier 2xx version.
I guess video drivers are no different than other software where older hardware is given no support consideration.
I used driver 275.33 for a long time on my GTX460 and and it worked flawless with VP11 and VP12. I have not tried it on VP13 but I am certain it will here too. You could try and use that driver but I am not certain if a GTS250 will actually improve preview or render performance. The GTX460 was just noticeable and you need to upgrade your hardware if you are interested in GPU acceleration. I use 2x GTX580 but even one of these from eBay will set you up nicely at a rather low cost.
I can't remember which driver version worked with my hardware and VP11, but it did give a dramatic increase in rendering speed even with my GTS-250 video card; something like 4:1 increase.
i7-860, 8GB
Windows 7 Ultimate, 64-bit (Service Pack 1)
DirectX version: 11.0
GPU processor:GeForce GTX 550 Ti
Driver version: 340.52
Direct3D API version: 11
Vegas pro 13.310
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Today I tried to render a Mainconcepts 12x7 1 pass and the nvidea driver crashed! That never happened before. I've often had issues with renders that would stop outputing data but never finish, and my share of Vegas crashes, this is my first nvidea crash ever.
How did you tell it was an NVidia crash rather than Vegas? I've seen lots of crashes where either the render freezes or just keeps running forever and ones where Vegas turns gray and announces it's died. How do you distinguish that the NVidea driver crashed?
As with any troubleshooting you do your best to isolate variables at work.
Let's say I have driver 1 installed and crashes in general are seldom.
Then completely remove driver 1 and install driver 2. For an NLE with GPU assist , the driver issues become part of the equation when you may find one part of the NLE working well and another part problematic say with a plugin.
This is ever so true with the combination of VegasPro and NewBlueFX - some driver and settings combination are acceptable to both, and otherwise the crashes get more frequent with one or another part of the variables of the entire system.
Update on my experience with the latest nVidia driver.
As I said earlier I tried a GPU render and it failed twice; the first time after about 2 minutes of rendering, the second time was immediately However, after looking at the thread for setting RAM preview size, I set the value to zero, and I was able to successfully perform GPU rendering on my hour long video twice in a row.
GPU render time took just over 34 minutes. CPU render time took just over 1 hour 2 minutes.