Adobe Reader XI: "Save As" function closes PDF automatically without saving

Hello,

I am using Adobe Reader XI on a Windows 10 operating system. My "Save As" function used to work completely normally until a few hours ago, but all of a sudden I find myself being unable to save any changes I make (i.e., annotations) to any of my PDF files. Whenever I click on the "Save As" option, the dialog box doesn't even open completely before the entire file closes automatically without saving anything, and I find that all changes have been lost when I reopen the respective file. I have not made any changes to any of the settings so I do not know what triggered this or how to resolve this issue. If I try to close a file after making a few changes to it, the "Do you want to save changes to your file?" prompt still shows up but as soon as I click on the "Save As" option, the file still closes automatically (once again without saving anything).

Some of the other posts on this website related to malfunctioning of the "Save As" option have suggested to go to "Edit > Preferences > General" and then uncheck the box that reads "Show online storage when saving files", however this last box does not show up at all in the "General" section of my "Preferences" window. 

I have lost several hours of work behind this malfunctioning and hence would really appreciate a solution that works. Thank you.