دلیل رخ دادن AccessViolationException؟؟؟

[saeed-kh]

سلام و نخسته.
میخوام 1024 بایت اول درایو رو بخونم.این کد قبلا رو ویندوز7 x64 م جواب میداد اما اینجا تو ویندوز7 x86 جدیدم تو خط آخر Exception میده!!!
int nread = 0;
uint handle;
byte[] buff = new byte[1024];
string driveRoot = string.Concat("\\\\.\\", driveLetter);
uint hRoot =CreateFile(driveRoot,
GENERIC_READ | GENERIC_WRITE,
FILE_SHARE_READ | FILE_SHARE_WRITE,
IntPtr.Zero,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
IntPtr.Zero);
if (hRoot != -1)
handle = ReadFile(hRoot, buff, 1024, nread, new System.Threading.NativeOverlapped());

AccessViolationException was unhadled.
Attempted to read or write protected memory. This is often an indication that other memory is corrupt.