Just ran into this problem last week, and couldn't find any information about this online.

The only MSDN forum solution I can find only suggests uninstall and reinstall SQL Server, which I did and still failed!

And I finally found the solution of this problem....

Turns out that the Microsoft.SqlServer.DataStorage.dll assembly is somehow replaced or misversioned in my GAC, due to some other installation I did in the past.

What I had to is to find another server that has working Management Studio 2008 on it, get the same assembly in that server and register it in my machine.

Once this is done the sql management studio should be working again.

Tim