First, think I'd get nasty and maually removing the contents of moodledata/cache and moodledata/localcache of all files folders contained there in. Safe to do as Moodle will rebuld those as needed.
If that dosen't fix ...
check web service error logs for clues.
and turn on debugging all the way to developer and share back here in this thread what it shows/reports ... uhhh, just the text. ;)
'spirit of sharing', Ken