Upload suddenly failing – target folder doesn’t exist

We have been using this plugin regularly and successfully for 7 years. Suddenly, today, files cannot be uploaded. The error message is: “Upload failed! Target folder doesn’t exist. File not allowed.”

I’ve checked the various files that have been attempted to be uploaded and there is nothing wrong with them. File size is low. The folder exists and is the same folder that’s been used for 7 years. Nothing has changed that I’m aware of. Upload was last used successfully 3 days ago. I’ve checked the server and there doesn’t appear to be any issues there. I’ve checked to see if the coding on the page changed for some reason and it hasn’t. I’m not sure where to look next to resolve this. Any suggestions would be appreciated. Thanks!