求助WriteFileEx返回错误代码87的解决办法

Question

异步存一个文件，程序相关代码：
//初始化
OVERLAPPED Overlap[2]
verlap[0].Offset = 0;
Overlap[0].OffsetHigh = 0;

//调用
WriteFileEx(theImagesFile_Info.Handle, InfoBuf[0], nBufBytes,
&Overlap[0], IoCompletionRoutine);
DWORD err=GetLastError();
//err=87;
theImagesFile_Info.Handle：文件句柄，打断点是正确的，InfoBuf[0]为开辟的内存，显示内存分配成功，nBufBytes为要写入文件的字节数，IoCompletionRoutine为回调函数。有知道错误在哪吗？谢谢