The missing plug-ins message often means that the file was created or edited in a newer version of the program. The only way to access it (if that is the case) is to have someone with the newer version to save it to IDML for you.
Missing links means that you need to find the original image files that were placed in the document at the time.
Does it open? I don’t think it would check for links if it was created in a later version.