I have been getting this error occasionally while trying to render using Magix AVC NVENC. This started with the most recent version of V15 and is happening in V16. It has occurred in the middle of Batch Render V2 script executions and individual render attempts.
Restarting Vegas gets me going again.
I didn't find anything about this when I searched the forum a few days ago.
Here is the error traceback I got a few minutes ago when it occurred in the Batch Render V2 script:
Windows 7, 64bit
32GB Ram
NVIDIA GeForce GTX 660 Ti