Okay, so you have embarked on a project that requires dynamically generating Microsoft Office Word documents based on a template Word document.
Naturally you have already added a Reference to the "Microsoft Word Object Library" to your project, by right-clicking on your project, Adding Reference / COM / Type Libraries / Microsoft Word Object Library.
I have the 15.0 version of the Word object library for my project.
You have written the appropriate C# server-side code to open the document, by using the "Documents.Open" method of the Word.Application object.
But hold on.
While everything works in your machine, it fails in the web server you deployed your application to.
You get the error message:
An exception of type 'System.NullReferenceException' occurred but was not handled in user code.
Additional information: Object reference not set to an instance of an object.
How can that be?
The answer is that Word failed to open the document because you did not have the proper permissions to do so.
Or rather, the user account which tried to open the Word document did not have appropriate access rights.
Below is the unintuitive solution for you.
Open the Component Services module from the Start Menu, or search for it.
You can manually start it from "C:\Windows\System32\comexp.msc"
In the Component Services window, expand the nodes to Console Root / Component Services / Computers / My Computer / DCOM Config
Under DCOM Config, scroll down to find "Microsoft Word 97 - 2003 Document" or its equivalent in your server.
Right-click on "Microsoft Word 97 - 2003 Document", select Properties / Identity.
In the Identity tab, change the option control selection from "The launching user" to "The interactive user".
Hit OK and Exit.
And voila!
Your frustrating error goes away, and your application magically works as you expected in your web server.
