Please note that Trial License does not work with full version of the question bank and vice-versa. So please make sure you are using the right version of the question bank. You may download the appropriate version of the question bank file from Downloads page.
The license is in plain text format. Some times, email programs try to format it when you view the email so please view the email as plain text while copying the license.
Usually, the error message is quite descriptive. So if it still does not work, please let us know the error message so that we can help.