The URL 'Shared Documents/file.pdf' is invalid. It may refer to a nonexistent file or folder, or refer to a valid file or folder that is not in the current Web

you wont be abl to load any files in the library/list

check the log files of sharepoint first.

if the logs say that for the database the 'PRIMARY' filegroup is full you will need to delete some data from that site. the primary file group size might be in few kbs and it wont allow you to delete any files from the sharepoint server also. if you are able to delete from the site start with very small size files and simultaneously clear them from the recycle bin.

check for disk space on sql server and then clear out the sql logs.