Authentication failed: Check your Credentials
The following error: AUTHENTICATION FAILURE provisioning ActiveSync: Check your credentials means you have entered in a password, user ID or server name incorrectly. Please run the quick configuration wizard in settings and check those fields for typos, stray characters, etc. The Android keyboards tend to autofill spaces, so please keep a sharp eye out for unnecessary spaces. You can also try leaving the domain field blank and entering your user ID like so: DOMAIN\jsmith.
Also, if you have recently updated your password, TouchDown will need you to change the current password to the new one as the app does not update this automatically. This is done by entering your new password on the Account tab. You can access the Account tab by tapping Menu, Settings, Account.