Salesforce Critical update :- https://eu1.salesforce.com/help/doc/en/salesforce_spring13_release_notes.pdf, page 88
Critical Update for rendering custom section names on page layouts is available in affected organizations. This update changes how custom section names in page layouts are rendered, to escape HTML tags and other markup. Prior to the Spring’13 release, custom section names in page layouts weren’t escaped, allowing the use of HTML markup and other tags. This wasn’t an intended feature, and the Escape Page Layout Section Names update corrects this behavior. With this update, tags in section names are escaped, and aren’t interpreted as markup in the browser.
Earlier it was working but due to above mentioned critical update its not working anymore.
Does any one has alternate solution for this??