[SP2010] Issue migrate Classic to Claims authentication

[SITUATION]
Currently I am working at a customer where we have to migrate SharePoint 2007 data to a new SharePoint 2010 environment. Security ACLs on the SharePoint 2007 data are registered in the old SharePoint 2007 way (called Classic in SharePoint 2010). In order to use claims these ACLs need to be converted into Claims ACLs.

[ISSUE]
On the TechNet site I discovered this article. Unfortunately when performing these steps (running a PowerShell script), it did not work. As with many issues, SharePoint doesn't give any clue what might be wrong :-(

[SOLUTION]
After some troubleshooting I remembered an issue I had back in MOSS2007. There I tried to perform an activity on a site collection, which did not work. It turned out that I did not have permissions on the site collection. To solve that, I granted myself "Full Control" permissions via the "Policy for Web Applications" page, after which the activity worked fine.

To test this theory, I tried the following steps:

1. Create a new web application
2. Create a new site collection
3. Add some data and set unique permissions
4. Grant my admin account Full Control permissions for the web application
5. Run the PowerShell script to migrate the web application to Claims

and see here, the script now runs just fine and migrates all Classic ACLs to Claims ACLs!!

[NOTE]
Microsoft has confirmed that there are some issues with the Classic to Claims migration. According to them, Service Pack 1 will include a tool which should be able to successfully migrate Classic to Claims. So either test your migration thoroughly or wait for SP1 (expected end Q2/beginning Q3)!!