For those who encounter this error during logging from CWA "Cannot sign in due to a server error. Please try again. If the problem persists, contact your system administrator."
This problem might be related to the CWAService account password expire. In the default configuration after your installation the CWAService account don't have the "Password Never Expire" option checked. You will need to set the password for the CWAService to never expire. Once this is configure, you will be able to login to CWA again