createFile invalid handle

I could use some help figuring out why createFile will fail on some machines and not on others. Customer's are installing a USB drive on their machines and then running my security application. The security app runs fine for most of the customer except for about 3. It fails every time with an invalid handle error. I have checked the owner and permissions on the drive letter and at the c:\ level and they are all fine. The code I am running is below.


snprintf(devpath, sizeof(devpath)-1, "\\\\?\\");
strcat(devpath, drive);

hDevice = CreateFile(devpath, // drive to open
//0, // no access to the drive
GENERIC_READ,
FILE_SHARE_READ,
NULL, // default security attributes
OPEN_EXISTING, // disposition
0, // file attributes
NULL); // do not copy file attributes


if (hDevice == INVALID_HANDLE_VALUE) // cannot open the drive
{
printf("E1129:Handle invalid\n");
printf("Press return key to continue.");
scanf("%c",answer);
return (FALSE);
}

Any thoughts as to how to fix this would be appreciated. I have actually added the GetLastError() call to the code to get the exact error code for the failure. I am now waiting on a customer call back to try the new code.