I'm really sorry that you're unable to send a picture message while abroad. Are you able to let me know if you can browse the internet at all in Tenerife?
If not, this will be the issue. MMS needs an internet connection to send. You can enable Data Roaming by logging into your online account here and going to Plans and Devices > Manage Services > Data Roaming.
Let me know how you get on with this I'm here if you need me.