XNua isn't the same as standard Lua, this is mainly in missing standard library functions (I know of no difference in the base language, but I suspect there are some bugs in weak references and metatables, if you find any log a bug please) such as assuming the parser is callable from the the VM. This lists some of the important differences. 

• Parser Functions - No dostring, dofile, loadfile etc. or anything that involves parsing a Lua file at runtime.
• GC functions - the Lua GC doesn't exist. Types are garbage collected buts its by the .NET CLR runtime and as such lifetimes and stats may be very different.
• io.* - not written yet
• maths.random - not written yet
• table.sort - not written yet
• os.* - all except time aren't written yet
• string.* - not written yet
• debug.* - not likely to ever exist
• various other minor standard functions
• Can't interface C# Event. Lua2IL provided a way of assigned lua functions to C# events, however this has been removed, as it used IL.Emit which doesn't exist on .NET Compact
• No lua source level debugging on Xbox 360 (for unknown reasons). Works well under x86
• The content pipeline way of getting a path for the lil files is dodgy as hell, but it appears to be a problem with the current content pipeline API. I've logged a feature suggestion on MS Connect
• Coroutines support is at best untested and possible broken