SSIS and Microsoft.Exchange.WebServices

Question

I am writing an SSIS package that has required me to use the Microsoft.Exchange.WebServices DLL. I have imported it into the VB Script Task where it is referenced from the following location:

C:\Program Files\Microsoft\Exchange\Web Services\2.0\Microsoft.Exchange.WebService.dll

The script task seems to 'like' it in so much that I have imported the Namespace and am able to declare the ExchangeService as an object. However, when it comes to running the package (both compiled and in debug) I get the following error:

System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Exchange.WebServices, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

I have checked the Regedit and can see that the DLL exists there... I am sure I am missing something silly... Is anyone able to help??

Thanks! Chris