Symptoms

Acronis True Image 2021 is installed on Windows 8.1 x64.

When you try to run an antivirus scan of the system, scan freezes and never finishes:

Cause

This issue is caused by a bug in Windows 8.1 thread scheduler.

Solution

Download and install Reliability improvement update for Windows 8.1 and Windows Server 2012 R2: May 2015