I've spent most of this evening trying to figure out why my Team Explorer was, all of a sudden, refusing to connect to the company TFS server - whilst the solution is not terribly exciting, this post serves to link the TFS symptom to the underlying problem.
Anyway, as I was saying, my attempts to add or connect to an existing Team Project resulted in a somewhat unhelpful "Team Foundation Error" message. Several reboots, uninstall/reinstall of Team Explorer later I was no better off, and Google wasn't much help either.
Earlier in the day I had also noticed that I was getting an error message when trying to use the 'Find' functionality in IE... this caused a rather odd-looking 'Error 49: Interface not registered' message.
On the premise that the problems might be related I decided to have a dig around... which soon revealed a solution courtesy of the veritable treasure trove that is www.jsifaq.com.
As the error message suggests, some of the IE components had become unregistered and the JSIFaq page (found here) listed the ones to re-register:
regsvr32 /s urlmon.dll
regsvr32 /s actxprxy.dll
regsvr32 /s shdocvw.dll
regsvr32 /s mshtml.dll
regsvr32 /s browseui.dll
regsvr32 /s jscript.dll
regsvr32 /s vbscript.dll
regsvr32 /s oleaut32.dll
After doing this, Team Explorer worked fine.... happy days - now to get back what I had intended to do this evening!