Iterating through a Lua table from C++?

I'm trying to load tables from Lua to C++ but I'm having trouble getting it right. I'm getting through the first iteration just fine but then at the second call to lua_next it crashes. Any ideas?

Lua file:

level = { 1, 2, 3, }

C++ file - First I did this:

lua_getglobal( L, "level" );
for( lua_pushnil( L ); lua_next( L, 1 ); lua_pop( L, -2 ) )
{
    if( lua_isnumber( L, -1 ) ) {
        int i = (int)lua_tonumber( L, -1 );
        //use number
    }
}
lua_pop( L, 1 );

Then I tried from the reference manual:

lua_getglobal( L, "level" );
int t = 1;
lua_pushnil( L );
while( lua_next( L, t ) ) {
    printf( "%s - %s", 
        lua_typename( L, lua_type( L, -2 ) ),
        lua_typename( L, lua_type( L, -1 ) ) );
    lua_pop( L, 1 );
}
lua_pop( L, 1 );

And finally this:

lua_getglobal( L, "level" );
lua_pushnil( L );

lua_next( L, 1 );
if( lua_isnumber( L, -1 ) ) {
    int i = (int)lua_tonumber( L, -1 );
    //use number fine
}
lua_pop( L, 1 );

lua_next( L, 1 ); //crashes

etc...

Naturally L is a lua_State* and I'm initializing it and parsing the file okay.

Edit: In response to Jesse Beder answer I tried this code, with a logger, but I still can't get it to work.

Log::Get().Write( "engine", "stack size: %i", lua_gettop( L ) );

lua_getglobal(L, "level");
if( lua_istable( L, -1 ) )
    Log::Get().Write( "engine", "-1 is a table" );

lua_pushnil(L);
if( lua_isnil( L, -1 ) )
    Log::Get().Write( "engine", "-1 is now nil" );
if( lua_istable( L, -2 ) )
    Log::Get().Write( "engine", "-2 is now table" );

int pred = lua_next( L, -2 );
Log::Get().Write( "engine", "pred: %i", pred );
while( pred ) {
    Log::Get().Write( "engine", "loop stuff" );
    if( lua_isnumber( L, -1 ) ) {
        int i = (int)lua_tonumber( L, -1 );
        //use number
        Log::Get().Write( "engine", "num: %i", i );
    }
    Log::Get().Write( "engine", "stack size: %i", lua_gettop( L ) );
    if( lua_istable( L, -3 ) )
        Log::Get().Write( "engine", "-3 is now table" );

    lua_pop( L, 1 );
    Log::Get().Write( "engine", "stack size: %i", lua_gettop( L ) );
    if( lua_istable( L, -2 ) )
        Log::Get().Write( "engine", "-2 is now table" );

    pred = lua_next( L, -2 );
    Log::Get().Write( "engine", "pred: %i", pred );
}
lua_pop( L, 1 );

Which gave this output:

stack size: 0
-1 is a table
-1 is now nil
-2 is now table
pred: 1
loop stuff
num: 1
stack size: 3
-3 is now table
stack size: 2
-2 is now table

Everything you said, Jesse, seems to hold true. But it still fails to go to the next iteration.

Edit2: I tried to copy the exact code into a new project, skipping all the surrounding classes and stuff I didn't bother to include here and there it works. But here it doesn't, and it will just survive one call the lua_next.

Edit3: I've narrowed it down a bit further now. I'm using hge as my 2D engine. I put all the previous code in the function test:

test(); //works
if( hge->System_Initiate() )
{       
    test(); //fails
    hge->System_Start();
}

As far as I understand hge doesn't do anything with lua. Here's the source code for a small test I made. The source for hge 1.81 is here.

Edit4: The question size is getting out of control but it can't be helped. This is the smallest code I've been able to reduce it to.

extern "C"
{
    #include <lua/lua.h>
    #include <lua/lualib.h>
    #include <lua/lauxlib.h>
}
#include <hge\hge.h>

bool frame_func()
{   
    return true;
}

bool render_func()
{
    return false;
}

void test()
{
    lua_State *L = lua_open();
    luaL_openlibs( L );

    if( luaL_dofile( L, "levels.lua" ) ) {
        lua_pop( L, -1 );
        return;
    }
    lua_getglobal(L, "level");
    lua_pushnil(L);

    while( lua_next( L, -2 ) ) {
        if( lua_isnumber( L, -1 ) ) {
            int i = (int)lua_tonumber( L, -1 );
            //use number
        }
        lua_pop( L, 1 );
    }
    lua_pop( L, 1 );

    lua_close( L );
}

int main()
{
    HGE *hge = hgeCreate( HGE_VERSION );

    hge->System_SetState( HGE_FRAMEFUNC, frame_func );
    hge->System_SetState( HGE_RENDERFUNC, render_func );
    hge->System_SetState( HGE_WINDOWED, true );
    hge->System_SetState( HGE_SCREENWIDTH, 800 );
    hge->System_SetState( HGE_SCREENHEIGHT, 600 );
    hge->System_SetState( HGE_SCREENBPP, 32 );

    //test(); //works

    if( hge->System_Initiate() )
    {       
        test(); //fails
        hge->System_Start();
    }

    hge->Release();

    return 0;
}