How to use Third Party dll in SharePoint Visual Studio 2010 web part ?

Hi,

I have added the following code on the Package.template.xml

<Assemblies>
    <Assembly Location="ThirdParty.dll" DeploymentTarget="GlobalAssemblyCache">
      <SafeControls>
        <SafeControl Assembly="ThirdParty, Version=5.10.0.0, Culture=neutral, PublicKeyToken=3E1E8E3744A5C13F" Namespace="ThirdParty" TypeName="*" Safe="True"/>       
      </SafeControls>
    </Assembly>
  </Assemblies>

& then added dll from advanced-->existing assembly --> from Gac-msil folder.

Even i am getting error, when i am deploy the wsp on other server, dll added correctly & safe control added in web config also. but web part doesn't appear, it is showing the "object reference not set to an instant of object" error.

Please advice.

Thanks,

Aasai