Optimizing PDF converts File into .tmp file

As the subject describes, optimizing PDF files yields the error message "The document could not be saved. Cannot save to this filename. Please save the document with a different name or in a different folder." and the file gets turned into a .tmp file. Optimizing the .tmp file and saving it to the previous name correctly saves it as a PDF, however, this wasn't necessary before. Due to the work environment, these files must stay within this folder and follow a certain naming convention that cannot be changed. Is there a reason these files keep converting into tmp files? Any help is appreciated. Thank you!