Debugging a C error handling function

["Ruan Kendall" <shearwater+lua@...>]

We're running a moderately complex application which is written in
C++, and uses lua scripts as event handlers, amongst other things.

I wrote a simple error handling function, which is uses as the error
handler by lua_pcall.

Under normal circumstances, it works just fine. However, under certain
circumstances (I'm not totally sure what all of these are yet) such as
C pcalls a lua script which calls a C function which pcalls a faulty
lua script, the error handler breaks. Even a totally empty error
handler like

int l_handle_error(lua_State* L) {
 return 0
}

still ends up generating a LUA_ERRERR error. No coroutines are involved at all

I'm not entirely certain under what circumstances ERRERR is returned,
and I haven't been able to gather this information from reading the
lua source.

Any advice?

 - Ruan