First, make sure you use the correct email address. If you still cannot log in, it's easiest to set up a new password on the "Forgot password?" Page. There you fill in your email address and get an email with a link. The link will help to create a new password to log in with.
If you still cannot log in please contact our customer service and we will assist you. Should the above options not fix the issue please, if possible, take a screenshot of what it looks like when the problem occurs and contact our customer service through our web form on the customer service page.