from as today.
I had the "there was an error downloading agreement" ERROR first,
As i have still windows XP i renamed my "cash" folder and "battle.net" folder in:
C:\Documents and Settings\All Users\Application Data\Blizzard Entertainment\Battle.net Renamed cash folder.
C:\Documents and Settings\All Users\Application Data\
Renamed my battle.net folder
then i tried again but got the error "There was a problem with an authentication module" instead.
so i switched back the renamed folders and moved the new made folder to other place.
Then i got the first error again.
also repaired diablo flushed DNS.
my room mate has no problem same internet connection other pc