title: Microsoft Office Interop Assembly references
body: <p>I have an application developed in Visual Studio 2005 which I am deploying using ClickOnce. My solution contains two projects - a user interface layer coded in VB, and a class library coded in C#.  My C# class library has some code that uses the Outlook and Excel Interop Assemblies (Microsoft.Office.Interop.Outlook and Microsoft.Office.Interop.Excel, both version 11). Here are my questions.</p>
  
  <ol>
  <li>Although I haven't found where this is stated as an absolute, my understanding is that you MUST have the appropriate versions of the Office applications (Outlook/Excel) in order to install an application that uses the Interop assemblies. Is this correct?</li>
  </ol>
  
  <p><strong>If (1. = Yes) Then</strong></p>
  
  <p>How would you handle the situation in which your application uses the Interop assemblies for only a couple of features that will be utilized by only a select few of the total user base? Why must I require every user of my application to install Microsoft Office if only some users will need to use those features? These Interop assemblies are just <em>.dll</em> files, so what makes them so different from others in that you can't just publish the file with your project and have that satisfy the reference regardless of what software is installed at the client? (Clearly I have a poor understanding of the GAC and it's effect on Visual Studio's behavior.) I would be happy to write my own code to check for the existence of the required Office software for the few features that use them. No Office, no access to feature...</p>
  
  <p><strong>Else</strong></p>
  
  <p>If my understanding on this is incorrect, then HOW do I setup my references and ClickOnce settings so that users don't encounter the following error upon installation attempt?</p>
  
  <p>"Unable to install or run the application. The application requires that assembly office Version 11.0.0.0 be installed in the Global Assembly Cache (GAC) first.</p>
  
  <p>Please Contact your system administrator."</p>
  
  <ul>
  <li>I have tried setting my Interop references CopyLocal property to both True and False. </li>
  <li>In my ClickOnce Application Files list, I have tried setting these assemblies to Include, Exclude and Prerequisite. </li>
  <li>In my research I have seen where some people have these references pointing to *C:\WINDOWS\assembly\GAC*, mine points to *C:\Program Files\Microsoft Visual Studio 9.0\Visual Studio Tools for Office\PIA\Office11* but I haven't found a way to change the reference path.  According to <a href="http://msdn.microsoft.com/en-us/library/ez524kew(VS.80).aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/ez524kew(VS.80).aspx</a> you CAN'T add references from the GAC, so how did other people manage it?</li>
  <li>I have tried copying the references from *C:\Program Files\Microsoft Visual Studio 9.0\Visual Studio Tools for Office\PIA\Office11* to my project directory and referencing them there.</li>
  </ul>
  
  <p><strong>End If</strong></p>
  
  <p>I suppose the main thing I need to know is how/if I can include these assemblies in my publication and satisfy or bypass the GAC requirement.</p>
  
  <p>Where possible, please try to answer my specific questions as directly as possible. While articles are helpful, I have already read A LOT of articles and tried A LOT of suggested solutions and have found no success. Keep in mind my lack of understanding of the logistics of how this all works to begin with.</p>
  
  <p>Forgive me for my lack of understanding, and thank you for any help you can offer. It is much appreciated!</p>