CSS Injector Error Message

I’m working on this site and need to modify the css. When i make modifiations and save the file, I’m getting this error. This has been going on for 2 days.

• Warning: file_put_contents(temporary://file6sHcQ7): failed to open stream: “DrupalTemporaryStreamWrapper::stream_open” call failed in file_unmanaged_save_data() (line 1936 of /data01/d7/dev.cmes.macmillan.yale.edu/includes/file.inc).
• The file could not be created.

And, below this red error message is the green message stating that my file has been saved, however, none of the modifications made are saved.