If your member isn't able to log in to their account, you need to ask your self the following questions and verify each of the questions to figure out the problem.
Does your member use the correct email?
Are there any typo errors on the email they are using? Whether it was on their end or yours.
Did your member enter the wrong password?
Are they using an uppercase instead of a lowercase?
If your member says that they've checked every possible solution, try logging in yourself as the member. Copy-paste the email you have on file and change their password. If you can connect to their profile you will then know that one of your questions didn't get verified correctly.
If you've modified their password, instruct you member to reset their password so they can retrieve their profile.