Like many of you, I often find that a map document that I have been working for hours become currupted. I finally got really frustrated this morning and contacted the ESRI New Zealand customer support and here is their response:
I have logged a call #159800 in regards to your question. Later this morning I will have a look at your document but in general map documents gets corrupted when using corrupted data or if properties of layer(s) reference wrong/missing fields or something similar. The recommend way is to recreate the map document from scratch adding data from the source and specifying all properties. Alternatively, you can add layer files if you have them but it has a certain possibility of corrupting the map if layer files reference wrong/missing fields.
Regards, GIS Technical Consultant Eagle Technology Group Ltd"
Surely, if this is the case, ESRI can handle the error more gracefully, for instance, in the same manner as a missing source file and open the map document anyway. Not being able a map document just becuase of a few missing fields/properties is absolutely a dissaster.