Unknown server tag 'asp:ScriptManager' after restoring content DB on new test environment.

I have created a new SharePoint 2007 Test environment on new machine in order to test/run SharePoint 2007 web application that is deployed on customer site production environment and functioning perfect. On SharePoint 2007 Test environment, First, I created a new web application (created successfully) then, i add/deployed all .wsp solution files that were required for that web application and then i restore contant DB. (restored successfully). When I access my test web application, it seems all the content were there as on customer production site, But many of the links did not work and it gives me following error:

An error occurred during the processing of . Unknown server tag 'asp:ScriptManager'. 
Troubleshoot issues with Windows SharePoint Services. 

i don't know how i fix this issue. Because i don't have access to actual code files web.config etc?

Any idea how to fix this issue?