I received the above error when I attempting to upload files to the Site Assets document library in my SharePoint 2013 site collection. My customer wanted to upload some files from another project into this folder. I thought, "This should be easy". And then this happened...
I first noticed this after I was able to copy a full folder of files but once I refreshed the folder, all of the files were no longer present. The document library was completely empty as if I had never uploaded anything. The size of the file didn't seem to matter.
I decided to filter on errors while uploading the files to see what my SharePoint ULS logs had to say. It appears my database is full.
If you are not able to upload files to a document library and receive the error that "It may refer to a nonexistent file or folder, or refer to a valid file or folder that is not in the web". You may also see the files that you upload disappear regardless the size of the file.
We should check the SharePoint ULS logs to determine if our database is full. We should then check the disk space on the SQL server and clear the SQL log files.