I can't open any kind of file through revit itsself. When I click on the "open" icon or the "file-open" pull down menue revit just freezes and no buttons work at all and I have to use task manager to shut revit down.
Interestingly when I click on the file I want to open in windows explorer revit will start up and I can access the file as normal. However I run multipal releases of revit and this means I'll end up upgrading a file that should only be worked on in an earlier release.

Please help.