Don't uninstall the previous version in your deployment task. It uninstalls any installed Virusscan 8.8, not the previous version.
Check in the full package and the patch into the Current branch.
The Update task will apply Patch 7 to existing devices, and the full install is there for deployment to devices which don't have virusscan already.
as philr said
if you created uninstall task it will un install any version. just create update task for existing systems and create deployment task for new or not having vse