CRM 4.0 upgrade: There is already an object named 'AttributeTypes' in the database.

This week I was helping a customer to upgrade their CRM 3.0 system to CRM 4.0.
The upgrade pre-check looks fine with all passed, no errors, no warnings.
But during the upgrade process, it first alert an error regarding C360, then I fix the problem, click the "Retry" button, it then generates another error:

" Microsoft.Crm.Setup.Server.InstallDatabaseAction failed.
System.Data.SqlClient.SqlException: There is already an object named 'AttributeTypes' in the database. "

That's very strange. But finally I found it's a design lack of upgrade process: The 'Retry' doesn't actually do 'Retry'!
So I had to:
1. Stop the upgrade process and uninstall CRM 4.0;
2. Restore CRM 3.0 databases, then install CRM 3.0 with existing databases;
3. Fix the problem which generated the first error;
4. Re-run the CRM 4.0 upgrade.

I did know there are some complains about C360 add-ons stop the CRM upgrade process, these could be the reasons:
1. The C360 uninstall doesn't do a clean uninstall all the time, so you may still see C360 icons on the CRM form, but no function;
2. Some C360 products create tables inside the CRM database which is not a recommended method, and again once you uninstall the product, the tables are still there.
3. C360 has a cleanup tool which does cleanup the remained infomation in the onLoad, onSave, and isv.cofig.xml etc. However, it doesn't cleanup the database. And the tool is hard to find on C360 website.

C360 provides some great add-ons for MSCRM, but we wish it could be better!