Writing USB Disk Sectors Results in Permission Error 5 - c++

Question

The code below is required by my app to write disk sectors of external USB drives. It works on most Win10 PCs, but it's returning error 5 for permission denied on a couple PCs. I have exclusions created for both Windows Defender and Malwarebytes. There's nothing in the event viewer related to the failure. The read function works without error.
I tried adding calls to FSCTL_LOCK_VOLUME and FSCTL_DISMOUNT_VOLUME, but this doesn't help. Probably not needed anyway since I'm accessing the physical disk after it's been cleaned, and not any volumes.
Any idea what could cause this, or how to resolve?
Would be great to learn if there's any alternate methods of reading and writing disk sectors.
BOOL Partitioner::BlockWrite(wchar_t* devIdentifier, unsigned __int64 lngStartbyte, DWORD bytesToRead, BYTE* buf)
{
BOOL ret = FALSE;
HANDLE devHan = CreateFile(devIdentifier, GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
if (devHan != INVALID_HANDLE_VALUE)
{
// Seek to the starting block to write
LARGE_INTEGER startByte;
startByte.QuadPart = lngStartbyte;
SetFilePointer(devHan, startByte.LowPart, (long*)&startByte.HighPart, FILE_BEGIN);
// Write the data (this is where error 5 is returned)
DWORD bytesWritten = 0;
ret = WriteFile(devHan, buf, bytesToRead, &bytesWritten, NULL);
FlushFileBuffers(devHan);
CloseHandle(devHan);
}
else
{
ret = GetLastError();
wchar_t msg[PATH_BUFFER_SIZE] = {0};
swprintf_s(msg, WCSIZE_FULL(msg), L"Error= %d, byte= %llu", ret, lngStartbyte);
mLog->LogError(msg);
}
return ret;
}

Answer 1

I found the answer where I wasn't expecting. I thought this had to be something related to how the file handles were being opened. Instead, turning off Real-time protection in the Virus threat protection settings for Windows 10 caused the error 5s to go away. To resolve without disabling real-time protection, you need to add an allowed app exclusion for each of the installed EXEs.
You can do this in code by scripting PowerShell:
string script = "powershell -Command \"Add-MpPreference -ControlledFolderAccessAllowedApplications '" + GetAppPath() + "\\AppServer.exe" + "'";
Process.Start(new ProcessStartInfo() { FileName = "cmd.exe", Arguments = "/c " + script, CreateNoWindow = true, WindowStyle = ProcessWindowStyle.Hidden }).WaitForExit();