Possible reason 1.
Please, make sure you do not add spaces when writing email and password. Also, make sure you write the same password you used to register in the web.
Possible reason 2.
If anyway you can access, please open the tool as administrator and try to access. Bare in mind that when you validate the email and password it not a login process. This process is to activate the license linked to your account. So, RiftGG has to access to some folders installed in your computer and if it has not permission, RiftGG can't validate the license.
Possible reason 3.
If you have tried everything and still can't access RiftGG, bare in mind that the license can is only activated in one computer only. So, if you already validated the licenses in a computer, you will not be able to activate it again. If you format the pc or delete the license, RiftGG will stop working.
If you are a RiftGG Freemium user and want another license, you can create another account or cancel the account that you have and register again.
If you are a user of RiftGG Premium and you would like to have another license, please contact firstname.lastname@example.org