Sharepoint 2010 Replacable Parameter not working

I have an aspx page in _layouts that is part of a package. It contains :

<%@ Assembly Name="$SharePoint.Project.As开发者_JAVA技巧semblyFullName$" %> 

This should be updated with the current assembly full name when I deploy - but it dont.

Anyone got any ideas?

So it turns out that the element needs to be included in the package - durrr. Silly me.