If you go into the my ACU section there is a box on the right hand side of the page called ask ACU, it may be worth asking about the problem your having through there. Other then that I'm out of ideas, sorry I couldn't of been more help.
My suggestion would be try to log into blackboard or your email to see if they work because the whole ACU system may not be recognising you for some reason.
Hi guys, when you try to sign in are you using a capital for the S in your number ie. S00012345, otherwise it wont work. The only other thing I can think of is if you have changed your password anywhere in the ACU site it will change for anything you try to log into.
Hope this helps :)