writeFile写磁带设备时为什么报87(参数错误)？

[walk_stop_walk]

调用的函数如下：
BOOL bRet = WriteFile(m_hTape,
(LPCVOID)(pBuf + iHaveWrite),
(DWORD)(iWriteFileLen - iHaveWrite),
(LPDWORD)&ulBytesWritten,
NULL );