ERROR_SERIAL_NO_DEVICE (0x0000045e) – Fix in 3 Steps

1. Driver mismatch – the most common cause

I've seen this hundreds of times. You plug in a USB-to-serial adapter or an internal serial card, and Windows throws 0x0000045E. Nine times out of ten, the driver version doesn't match the chipset on your device.

The usual trigger: you just updated Windows, or you plugged the device into a different USB port. Windows Update sometimes replaces a working generic driver with a newer one that doesn't speak your hardware's language. The result? ERROR_SERIAL_NO_DEVICE.

What to do

1. Press Windows key + X and select Device Manager.
2. Expand Ports (COM & LPT). Look for your serial device—it'll be labeled something like "Prolific USB-to-Serial Comm Port" or "FTDI Serial Port."
3. Right-click that device and choose Properties.
4. Go to the Driver tab. Click Roll Back Driver. If the button is grayed out, that means no previous driver exists—skip to step 7.
5. When it asks why you're rolling back, pick "My device stopped working after a driver update." Click Yes.
6. After it finishes, you should see the port name change from "Port_#0001" to something recognizable. Windows will reinitialize the device—give it 10 seconds.
7. If rollback isn't available, click Uninstall device. Check "Delete the driver software for this device" and click Uninstall.
8. Restart your PC. After boot, Windows will reinstall the default driver. If 0x0000045E still shows up, go download the correct driver from the chipset manufacturer's site (Prolific, FTDI, or Silicon Labs) and install it manually.

After step 8, open your device software again. The error should be gone. If not, move on to the cable.

2. Bad cable or loose connection

Serial cables die. Especially the cheap ones with molded connectors that hide broken wires. I've pulled apart dozens of those—the solder joints inside snap from the tiniest bend.

The telltale sign: you get the error intermittently. One minute the device works, the next you get 0x0000045E. Or it works when the cable is held in a certain position and fails when you let go.

Test your cable

1. Swap the cable with a known-good one. If you don't have a spare, test the current cable with a loopback plug or a multimeter.
2. If you're using a DB9-to-USB adapter, check the DB9 connector's pins. One bent pin can cause this exact error. Use a bright light to examine each pin from the side—don't just look head-on.
3. For internal serial ports on older PCs (like a motherboard header), reseat the cable on the motherboard side. Those 10-pin headers are notorious for coming loose. Unplug it, inspect for dust or bent pins, then push it back on firmly.
4. Still stuck? Test with a different serial device. If the error only happens with one specific gadget (like a barcode scanner or a CNC machine), the fault might be in that device's serial port, not your computer.

If swapping the cable fixed it, you're done. If not, the issue is on the PC side—most likely a driver conflict leftover from a previous device.

3. Dead or disabled serial port

This one's rare but easy to miss. The physical COM port on your PC—or the virtual port created by a USB adapter—is actually dead, disabled in BIOS, or using an IRQ that another device has already claimed.

Real scenario: a user plugged their USB-to-serial adapter into a front-panel USB port that had a bent pin inside. Windows detected the adapter but couldn't initialize the serial engine. That's exactly 0x0000045E.

Check and re-enable the port

1. Open Device Manager again. Look under Ports (COM & LPT) for any device with a yellow triangle or a down arrow.
2. If you see a down arrow, right-click the device and select Enable device.
3. Still no luck? Right-click the device, choose Properties, then go to the Port Settings tab. Click Advanced. Under COM Port Number, change it to a different unused port (like COM3 or COM5). Windows will reassign the port and reinitialize the driver.
4. If you're using an internal serial port on a desktop, reboot into BIOS/UEFI (press Del or F2 on startup). Look for Onboard Serial Port or COM Port settings. Make sure it's set to Enabled and not Auto or Disabled. If you find it set to a specific I/O address (like 3F8h/IRQ4), leave it—that's fine.
5. For USB adapters, try a different USB port—preferably one on the back of the PC that connects directly to the motherboard. Front-panel ports often have poor shielding or voltage drop that kills serial initialization.

After any of these steps, restart your PC. The serial device should initialize cleanly now.

Quick-reference summary

If none of these work, the serial chip on your device may be fried. That's rare—I've seen it maybe four times in ten years. More often, it's a bad driver update or a wobbly cable. Start with the driver, test the cable, then check the port. You'll get it.