Describe the Issue
I am having this same issue. At first i thought it was because my saves were at max so I opened the folder with the game running and deleted half my saves to no avail. I then ended up moving to another area so it would Autosave, then quit the game. Here is all the files you may need for this issue. I noticed that if i quit the game, then reopen it I can save again. Not sure why this is.
Steps to Reproduce the issue
1) I open the menu
2) I click save on new save (Don't get a response)
3) I click save on an old save
4) It asks if i am sure, and i click yes
5) It closes the dialog box but does not save
Important files
DxDiag.txt
output_log.zip
I'll email saves as it says they are to large to upload even when zipped.