Here are two steps that you need to do to the component to make it run in a partial trust.

1. Remove strong naming as it's not needed
2. Add APTCA (AllowPartiallyTrustedCallerAttribute) to the component

You can adjust your component by using the two steps above, or contact your vendor to update their component to run in medium trust.  Leaving your component running in full trust leaves your site and the web server it is located on highly vulnerable to security holes. 

MS article regarding APTCA:  http://msdn2.microsoft.com/en-us/library/d18a6dca.aspx.