Its a long shot, has anyone used Esri ArcObjects recently?
According to the docs:
A new requirement is runtime binding. Runtime binding refers to locating the appropriate ArcGIS product installation of a stand-alone ArcGIS Desktop or Engine application before any ArcObjects code (including license initialization) is called. The application programming interfaces (APIs) to establish runtime binding are in the ESRI.ArcGIS.RuntimeManager class in the ESRI.ArcGIS.Version assembly
But I cannot find ESRI.ArcGIS.Version.dll anywhere. I have the trial version of ArcMap 10.1. Does anyone know how I can get hold of this DLL?
ArcObjects is the ArcGIS API, not part of ArcMap. You use it to build GIS applications using ArcMap's engine, but you need more than just ArcMap to do it. Unfortunately it costs money to get hold of ArcObjects - the bit you're looking for is ArcGIS Engine:
http://www.esri.com/software/arcgis/edn/what-you-get
Of course, it depends what you're trying to do - if you want to do some custom coding inside ArcMap, you may be able to do it with ArcPy:
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//000v00000001000000