I have the same issue here
Just started using calibre ( which , of course means , just started learning calibre)
good to see I wasn't the only one with this issue
sometimes the metadata is updated right away and no problem, more and more , I get the error listed in the post above
WARNING: There were errors: There were errors downloading social metadata
Amazon
Traceback (most recent call last):
File "site-packages\calibre\ebooks\metadata\fetch.py", line 219, in fetch
File "site-packages\calibre\ebooks\metadata\amazon.py", line 39, in get_social_metadata
File "site-packages\mechanize-0.1.11-py2.6.egg\mechanize\_mechanize.py", line 209, in open
File "site-packages\mechanize-0.1.11-py2.6.egg\mechanize\_mechanize.py", line 261, in _mech_open
httperror_seek_wrapper: HTTP Error 404: NOT FOUND