: The major security update KB5074109 (released January 2026) removed four legacy inbox modem drivers: agrsm64.sys, agrsm.sys, smserl64.sys, and smserial.sys . This deliberate security move affects older Agere/LSI and Motorola soft-modems. Users reported dial-up and telephony modems stopped working, even some sold as "Windows 11 compatible".

While it may look like a system error, this is usually a harmless side effect of how Windows handles mobile device services like the Microsoft Phone Link app . Why the SMS/MMS Driver Appears

Visit the official website of your device manufacturer (e.g., Lenovo, Dell, HP).

: If you use a laptop from a brand like HP or Dell , tools like the HP Support Assistant or Dell SupportAssist can occasionally find the missing protocol drivers for you.

If you only need to text from your PC and drivers remain an issue, you can use Google Messages for Web in your browser. This requires no local drivers as it connects to your phone via the cloud.

Unlike a graphics driver, the "SMS/MMS driver" isn't usually a single file labeled "SMS.sys." Instead, it is a component of the driver package that allows Windows to communicate with the modem's messaging service 1.2.3 .

If you see a yellow exclamation mark and don't need to text from your PC, the easiest fix is to disable the service that triggers the driver request. Control Panel and select Devices and Printers Locate your paired mobile device , right-click its icon, and select Properties Uncheck the box for

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If the driver is glitching, forcing a reinstall via Device Manager can fix it. Right-click the and select Device Manager .

Click . Scroll down, select Bluetooth , and click Next . In the left column (Manufacturer), select Microsoft .

phones or tablets—to your Windows 11 PC via Bluetooth. Windows detects that your phone is capable of sending messages (the Message Access Profile, or MAP) and tries to find a specific driver to "manage" that capability locally. Why It Stays "Unknown"

To help you diagnose these issues, here is a quick look at the most common problems:

Right-click and select , then restart your PC and pair your phone again through the Phone Link app to reinstall fresh virtual drivers. Summary of Key Windows 11 Cellular Drivers

If the driver appears faulty (yellow exclamation mark), select , restart your computer, and let Windows reinstall it automatically 1.2.3. 3. Install Manufacturer Chipset Drivers