Hello,
EWS often requires including a domain name in the actual server login, such as:
If your email is user@corp.com, the login could be something similar to: "corp/user@corp.com", "corp/user", "global/user@corp.com"... the domain could be even something like "mid_west_sales_dept/user@corp.com"... There really is no way for the app to guess which it is.
Could you try a couple of these variations and if it doesn't help, ask your Exchange admin about this?
Feel free to create a debug log too (see my sig below).