The most common reason for seeing this message is a conflict between your @my.acm.ac.uk email address and a personal @gmail.com or @googlemail.com email address.
Note: YOU WILL NOT BE ABLE TO ACCESS CANVAS WHILE LOGGED INTO YOUR PERSONAL GMAIL ACCOUNT.
Step 1. Log into your ACM Gmail account (log out of any personal Gmail accounts first)
Step 2. Go to https://m.acm.ac.uk/
Step 3. Log in using your ACM email address and password (clicking on 'Student Login' might work too)
Step 4. On the myACM dashboard click on the Canvas icon.
If you have forgotten your ACM Gmail password please email firstname.lastname@example.org to reset.