this account needs to be converted to a battlenet account

i've been playing warmane servers for a couple years, and i've been on frostwolf for the last couple months. occasionally, i get the message "this account needs to be converted to a battlenet account...", but if i just try a few times, or just switch back and forth from one account to the other, it repairs itself.

tonite, i've been trying for a couple hours. i've checked the config file, all looks fine there. i've tried switching back and forth from account to account, but i'm getting the error on both. i've restarted the game many times, and even reboot my computer a couple times. any other ideas?

thanks in advance for your help!