In TFS 2010, the security permissions have been re-arranged. This means that for your upgraded projects, users who are project administrator no longer have permissions to manage the build by default.
To change this permissions, you’ll have to open up the project in Team Explorer, right-clicking Builds, and then clicking Security. You can apply permissions to a specific build definition by right-clicking the build definition and then clicking Security. If you want to apply permissions to a build folder, right-click that folder, and click Security. Additionally, you can set these permissions by using the TFSSecurity command-line tool.
More information on the MSDN website.