GoDaddy by default runs sites under medium trust which means that you cannot have an unsigned/untrusted dll.
You can ask them to run your site under full trust, but they probably won't.
You can sign the dll (or if you got it from someone/someplace you need to get a signed version
here is more info on medium trust sites:
http://msdn.microsoft.com/en-us/library/ms998341.aspx