The license is in plain text format. Sometimes, email programs try to format it by inserting new lines while displaying the email, this causes ETS Viewer to not recognize the license. Please view the email as plain text while copying the license. You can also do "view source" on the email to see the license key in original format.
We also attach the license key as a zip file attachment with the email that we send after processing your order. You can extract license.txt from the zip file, open the text file in notepad, and copy the license.
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 our Help/All Downloads page.
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.