When installing Sonicwall NetExtender 8.0.241 or later on Windows 7, you may get the following error:

"Damaged version of net extender detected on your system. Please re download net extender"

The reason for this error is you probably are missing Windows Update KB3033929, which adds SHA256 support into Windows. Because SHA256 certificates are now the new norm, the latest Sonicwall certificates also use this hashing algorithm. Without the update, Windows 7 and Server 2008R2 do not have support for SHA256.

You can resolve the issue by installing the update, then reinstalling NetExtender:

1. Download and install KB3033929.
2. Uninstall Sonicwall NetExtender (via Control Panel).
3. Delete the program directory left over after the uninstallation: C:\Program Files (x86)\SonicWALL\SSL-VPN\NetExtender
4. Re-install NetExtender, and reboot after the installation.

Source: https://support.sonicwall.com/sonicwall-secure-mobile-access/kb/205362