Can't connect to Battle.net on Warcraft 3

i downloaded Warcraft 3 digitally on vista, and when i start warcraft 3 everything works fine except when i click start battle.net i get an error saying

"There was an error writing to your hard drive while trying to download a file from battle.net. you may need to free some space. please check your hard drive and try again."

and i have over 168gb left out of 298gb

please help