You are unable to log into Marketo because you need to be authorized on your device.
Marketo tracks authorized devices by IP. If you are logging in from a different network, such as a home or hotel network, your IP will be different and you may need to authorize or re-authorize your device. Also, some networks assign IPs dynamically, so even if you are logging in from a location and device you have used before, the IP address may have changed and you would need to re-authorize the device.
You should receive an email with a code that allows you to authorize and log in. If for some reason you are not able to do so, please contact support and we can authorize your device for you.
Another option would be to disable the IP restrictions in the Admin panel: Admin > Login Settings > Edit IP Restrictions.