[Attilitus]

Then in the template file "header" for the "TestSite_Beta" template

I do not understand what this means.

My provided code will make the variable {vb:var variable_name} available in the template with name 'template_name'. If the template in which you are adding the variable is not named exactly 'template_name' then the variable will not be accessible from that template.

Perhaps this is your problem:

Note that once a template is parsed, all non-registered variables are removed from the template string. That is: If you have two templates: template1 and template2. Then suppose you render template1 and store it in variable var_template1, then put {vb:raw var_template1} in template2. Registering a variable for template2, will not allow you to use that variable in template1.