Word documents fail to save on Mac

Occasionally when i click save on my word document it says that the file already exists and asks if i would like to replace it and this error occurs continously whenever i hit the save icon.

To prevent this i have resorted to saving the document under a new name so it doesn't try to replace the old one, however the problem soon returns and i end up in the some cycle of renaming it.

Any suggestions on how to prevent this problem?