I am suddenly getting this too - have the newest version 1.3.10. Newest Nvidia beta driver. Tons of mods. Latest skse, Tesval.dll and the list goes on. skyrim character manager, skse_loader ... the works. What I did notice is Skyrim starts the first time every time when I reboot. So I reboot. This leads me to believe it is one of the drivers. On the other hand with the new versions of everything my frame rate is now through the roof. So I have that going for me.