Every time I go to one cell I get a Beep and an error message

X Assert

file c:\_Skyrim\Code\TesV\BShade\Shades|BSLightingShaderProperty.cpp Line 806

It gives an option to Ignore or Retry. I've been Ignoring it.

I don't see any problem when I go into that cell in game but I would like to fix this if possible. Any idea what is causing it?