It take a bit of time to get it to work, Android and iPhone don't have a fully compliant Exchange client so it just takes a bit of time to trick the server onto letting you on - but once you've signed in the first time you're alright.
Which devices are you trying to use and which software versions are you using?
The correct format is that your username is the full Aston email address, and the password is as it is for MAP/Blackboard/ISA