I do know I had some problems with the update to 17.1.178. You may want to run a repair of the application.
Control Panel |Unintstall or Change program | Click on Mindjet Manager 2017 and select Repair.
The alternative is to go the Mindjet Website and down a full copy of the program re-install.
That should do the trick.
Can you, do a save as and save the "problem map" with a new name. Test to see if the renamed map will open and if it is workable.
See if that allows you to edit the map with a new name.
Jerry, I found a Workaround due to your Input: I did Export opd maps into an opml file and then re-Import it. These were files created on an older Version of the program on my former Laptop. After re-importing the opml file it works and I am able to edit the file. Just loosing all the formatting.