This error will occur if the number is:

1. No longer a live number

2. Not recognised from the way you have entered it inside the contact record profile i.e. +44 (0) 1793 343433 - You need to remove the brackets around the zero as this is not recognised in the number.  

By removing the brackets so that the number now displays as +4401793 343333 will work correctly and the error message will no longer happen.