I get the same problem, the error console seems to have the same error as in the webmail log file:
HttpComms3.js: send : Exception : NS_ERROR_XPC_CANT_GET_PARAM_IFACE_INFO. Error message: Cannot find interface information for parameter arg 1 [nsIWebMailCookieManager2.findCookie] 354 Hotmail-SR-BETA: logIN : Exception : Error. Error message: httpConnection returned false 147 Jon
