Recently we had an issue when trying to reinstall TMG 2010 onto one of our servers.
When we ran the installation wizard it failed with the following error “Error installing TMG 2010 failed to install SQL Express 2008 (reporting instance”
To resolve this we had to do the following
- Uninstall SQL 2008 Native Client
- Delete the following folders “Microsoft Forefront Threat Management Gateway and Microsoft SQL Server” from Program Files and Program Files x86
- Reboot your server
After the reboot everything worked fine