It looks like the variable ESO_version isn't defined. You could put a line before line 214 like this:
Lua Code:
if ESO_version == nil then ESO_version = "" end
But that would just be a band-aid solution I think. Perhaps your variable name is slightly different from what you were expecting? Or it's actually part of a table, not a standalone global? Try to find where in the code this variable is/should be defined.