How can I reference a dll in the GAC from Visual Studio?

Registering assmblies into the GAC does not then place a reference to the assembly in the add references dialog. You still need to reference the assembly by path for your project, the main difference being you do not need to use the copy local option, your app will find it at runtime.

In this particular case, you just need to reference your assembly by path (browse) or if you really want to have it in the add reference dialog there is a registry setting where you can add additional paths.

Note, if you ship your app to someone who does not have this assembly installed you will need to ship it, and in this case you really need to use the SharedManagementObjects.msi redistributable.

In VS, right click your project, select "Add Reference...", and you will see all the namespaces that exist in your GAC. Choose Microsoft.SqlServer.Management.RegisteredServers and click OK, and you should be good to go

EDIT:

That is the way you want to do this most of the time. However, after a bit of poking around I found this issue on MS Connect. MS says it is a known deployment issue, and they don't have a work around. The guy says if he copies the dll from the GAC folder and drops it in his bin, it works.

Assuming you alredy tried to "Add Reference..." as explained above and did not succeed, you can have a look here. They say you have to meet some prerequisites: - .NET 3.5 SP1 - Windows Installer 4.5

EDIT: According to this post it is a known issue.

And this could be the solution you're looking for :)

The relevant files and references can be found here:

http://msdn.microsoft.com/en-us/library/cc283981.aspx

Note the links off it about implementation/etc.