There is a deadlock in the object cache when multiple packages are updated within a nested transaction. This means that any solution that installs multiple packages may hang during uninstall.
This issue is resolved within Notification Server 6.0 SP3 Rollup Pack 6. This Rollup Pack has been superseded and all fixes are included within the latest Rollup Pack.
Symantec recommends installing the latest rollup pack via the Solution Center found at Configuration > Upgrade/Install Additional Solutions.
Release notes can be found at KB article ID 34317
Notification Server 6.0 SP3 (6.0.6074)
SQL Server 2005