Here's a fix to the problem: delete the .suo files.
My attempts to open solution included: (1) System hard and soft re-boots ; (2) Getting the latest version of the solution from Team Foundation Server; (3) Rolling back changes I had made; and (4) eliminating Visual Studio Add-ins such as Jet Brains Resharper (ver sion 4.5). None of these helped. Blog post and information I found on forums about this issue do not reveal a consistent resolution to the problem (with some folk even reinstalling Visual Studio 2008 and the service packs; others removing and adding references from projects; or removing and re-adding projects in the solution).
I deleted the *.sou file for the solution and I was up and running sans my break points and bookmarks. So maybe the .sou file had become corrupted or Visual Studio was not able to deal with some combination of the elements it stores. Who cares? I was going again! Hopefully this might serve as a quick first option to resolve the issue for those who encounter it