Yahoo! in mail app keeps asking for password
I have my iCloud email, and gmail set up and there is never a glitch, why does my yahoo continue to pop up and ask me to reenter my password, i have erased and re entered the account twice now and it always happens, i even saved the password in the keychain, why does yahoo not work. it never has this problem on my iPhone.
iMac, Mac OS X (10.7.3)