Thank you for your post.
Obviously, something has changed, so let's try moving the file to the local machine and try opening it. If the file does not open on the local machine, then there may be something wrong with the file. Remove the local machine from the network and try again. If it still doesn't open, then there is something wrong with the file. If the file does open, then you can start looking at what is occurring on the network, or check the server for read/write privileges, etc.
Please keep me posted to what you find. This may help other users who encounter the same problem.