Multicam won't start or closes abruptly: Smart App Control

Symptom

On some Windows 11 PCs, Multicam Suite refuses to start, or closes a few seconds after launch. The Multicam log (C:\ProgramData\MultiCam\Logs) contains error code 0x800711C7 or the message "An Application Control policy has blocked this file", often on MPLATFORMLib.dll.

Cause

Windows 11 includes a protection called Smart App Control. It blocks programs it doesn't recognize that carry no digital signature. Current versions of Multicam Suite are not signed yet, so Smart App Control blocks some of their files.

Since the 2026 Windows updates, this protection can be turned on for an existing PC, not only on a fresh Windows installation, so more PCs are affected.

A signed version of Multicam Suite is on the way. Until then, the workaround is to turn Smart App Control off.

Workaround: turn Smart App Control off

You need an administrator account on the PC.

1. Open the Start menu, type Windows Security and open the app.
2. Click App & browser control.
3. Click Smart App Control settings.
4. Select Off.
5. Restart Multicam.

Turning Smart App Control back on later

Once the signed version of Multicam Suite is installed, you can turn Smart App Control back on in the same place by selecting On.

If the On option is grayed out, this is a known issue with Windows update KB5127648 (October 2026), which Microsoft is fixing in a later update. Install the latest Windows updates and try again.

PCs managed by an IT department

If your PC is managed by your IT department (an application control policy such as WDAC or AppLocker), don't change anything yourself: send them error code 0x800711C7 and contact our support, who will tell them how to allow Multicam Suite.