When installing an older installer in Windows 10/8 that does not support older SUM3D libraries, SUM3D may go down randomly. To fix it, follow the instructions below.
1. Find the _RegDeregistra_LabShellExt_xSUM zip file in the SUM directory.
2. Copy it into the x64 folder and extract the zip.
3. Cut both Deregistra files and move them into the x64 folder.
4. Right-click and run both _deregistra files as admin, which will unregister the labshell extension.