I created a few customized Content Types in the site and enabled “Manage Content Types” in document library. Now when user creates new files from the template and save it, a javascript error will pop up in DIP window: “‘length is null or not an object”. Microsoft confirmed it’s a SharePoint bug and now finally have [...]

Read the complete post at http://sharemypoint.wordpress.com/2008/04/11/got-javascript-error-after-enabled-content-type/