Comment 1 for bug 315896

Performing automated upgrades across major revision numbers of a program isn't recommended.

There are a large number of changes in the configuration files and in their processing from version 1.1.x to version 2.1.x. Writing scripts to do automated upgrades is extremely difficult. The upgrade process MUST be done by hand.

My suggestion is that the 2.1.x installer check the major version number of the previously installed package. If they don't match, it should refuse to do the upgrade.