If you have troubles log in, try to reset your password. The most probably case is that the invitation you had has expired.
How to reset your password
Go to the dashboard log in page:
After the "Login" button, you will have a question "Forgot your password?":
Just click on it, add your email and click "send Password". This window will appear:
An email should appear in your inbox. Remember to check the spam mail, maybe it is there.
Click on "change my password" and you will be redirected to a form that allows you to create a new one:
Just click "reset" and try to log in in the Dashboard with the new one 