If you are able to print a registration card from the guest profile, but not from the reservation card in the Reservation overview section, then it could be that there is no companion listed in the reservation:
To solve this go to the reservation and add a companion via the Groups tab:
We would also recommend you checking your extension, as some of them might be causing this error, too. For example, open: chrome://extensions/ and check whether or not the McAffee WebAdvisor extension is on. If so, you might need to switch it off, as it is blocking some content in Mews. We would highly recommend you to reach out to your IT Team, to check if it is safe to switch it off.
If you need to keep this extension on, then we suggest printing the registration card from the Incognito mode in your browser.
You can find more information on