Unity 4 hangs when opening Visual Studio 2008?

I recently upgraded to Unity 4, and have my code editor set to Visual Studio 2008, which worked fine in Unity 3.x. However, when I double-click a script or a error message in the console, Unity just freezes, and doesn't even bring up the "opening Visual Studio" dialog it used to. I then just have to kill Unity.

If I have my script editor set to MonoDevelop, there are no such issues. Is this a common problem, and are there any solutions to it? Thanks!