Hi Brian,
You may be trying to open an MXD from a later release of ArcGIS Desktop (i.e. 10.6). Do you know what version this MXD was created in?
Thanks for your reply Jake. I fixed the problem using MXD Doctor utility. You are correct, it was created in an older version and opened and saved it in a newer version. I found this video to be very helpful. Convert MXD File to Old Version (MXD Doctor) - YouTube Do you know how to prevent this in the future?
It would be best to keep everyone at the same release of ArcGIS Desktop.
Yes, this would certainly help for teams. This is a situation where I opened an older file I had created, made edits, saved in the newer version, and was subsequently unable to open again. I presume I will have to repeat this conversion process with any older file.
If you're making edits to the data (i.e. creating/updating/deleting features) you won't have to save the MXD afterwards, just save your edits. However, if you are making changes to a layer (i.e. adding labels, changing symbology, adding an additional layer), then yes you will need to save the MXD.
I had the exact same problem. Strangely enough, the file opened perfectly normal if I first started ArcMap and then opend my mxd from inside the program.