Files with the .MSD extension contain published maps based on the MXD map document format which have been placed on an ArcGIS Server, which in turn makes the map available for real-time online viewing. MSD files are created by the ArcGIS Desktop software version 9.3.1 and above, part of ArcGIS software, which is meant for creating maps and processing various type of geo-spatial data.

TIP: You can change extension of your MSD file from .MSD to .ZIP and extract by some archiving software (e.x WinZip). You will see component .XML files what can help you with incorrect data paths debugging.