Usually these error messages mean that your phone is operator locked and it is not acknowledging the new SIM.
In this case, unfortunately you will not be able to make use of the SIM. Contact your phone operator and ask them to unlock the mobile, if possible. You could also try and insert the SIM in another phone to see if that works - if you confirm that the SIM is working properly, you could potentially borrow another phone or mobile device to use while you're abroad.
Alternatively, you could be out of the coverage area for the network. This is pretty common in larger countries like the US, Canada and Australia, where complete network coverage of rural areas is rare.
If neither of these causes apply to you, please contact us at firstname.lastname@example.org, we’ll look into it and get back to you.