Lua PANIC error

我正在用c++创建一个数独求解器，同时实现用于实际解决谜题的Lua脚本。我已经创建了以下Lua代码，但得到一个

PANIC:调用Lua API时未受保护的错误(尝试调用nil值)

错误。在SciTE中编译代码时，我得到以下错误:

lua: SudokuSolver。Lua:99: 'end'预期(在第61行关闭'for')附近的"

在第61行有for循环的函数末尾添加三个'end'可以清除该错误，但会在c++程序中导致错误。有人可以看看我的Lua，看看是否有任何语法错误或其他问题，可能会导致这一点?谢谢你

-- Table Declaration
SudokuGrid = {}
function RecieveGrid ( _Pos, _Value )
    -- Recives the cell value at _Pos position from C++
    SudokuGrid[_Pos] = _Value
end
function SolveSudoku ( _Pos )
    -- Recursive function which solves the sudoku puzzle
    local iNewValue = 1
    -- If Position is 82+, all cells are solved
    if( _Pos >= 82 ) then
        return true
    end
    -- If Position already has a value
    if( SudokuGrid[_Pos] ~= 0) then
        return SolveSudoku( _Pos + 1 )
    else
        while(true) do
            SudokuGrid[_Pos] = iNewValue
            iNewValue = iNewValue + 1
            -- If the new value of the cell is higher than 9 its not valid
            if( SudokuGrid[_Pos] > 9 ) then
                --Reset value
                SudokuGrid[_Pos] = 0
                return false
            end
            if( IsValid( _Pos ) and SolveSudoku( _Pos + 1 ) ) then
                return true
            end
        end
    end
end
function IsValid ( _Pos )
    -- Calculate Column and Row in Grid
    x = _Pos % 9
    if( x == 0 ) then
        x = 9
    end
    y = math.ceil(_Pos / 9)
    -- Check Rows
    for i=1, 9 do
        CheckVal = ((y - 1)  * 9) + i
        if( CheckVal == _Pos ) then
            -- Do nothing
        else if ( SudokuGrid[_Pos] == SudokuGrid[CheckVal]and SudokuGrid[_Pos] ~= 0 ) then
            return false
        else
            -- Do nothing
        end
    end
    -- Check Columns
    for i=1, 9 do
        CheckVal = ((i - 1) * 9) + x
        if( CheckVal == _Pos ) then
            -- Do nothing
        else if ( SudokuGrid[_Pos] == SudokuGrid[CheckVal] and SudokuGrid[_Pos] ~= 0 ) then
            return false
        else
            -- Do nothing
        end
    end
    -- Check 3X3 Grid
    SquareCol = math.ceil(x/3)
    SquareRow = math.ceil(y/3)
    StartVal = (SquareCol - 1) * 27 + (SquareRow * 3) -2
    for j=0, 2 do
        for i=0, 2 do
            CheckVal = StartVal + i
            if( CheckVal == _Pos ) then
                -- Do nothing
            else if ( SudokuGrid[_Pos] == SudokuGrid[CheckVal] and SudokuGrid[_Pos] ~= 0 ) then
                return false
            else
                -- Do nothing
            end
        end
        StartVal = StartVal + 9
    end
    return true
end
function SendGrid ( _Pos )
    -- Sends the value at _Pos to C++
    return SudokuGrid[_Pos]
end