If a user enters numerics in their Forename / Surname field should this trigger the validation - the same as would occur if Alpha characters were entered in a Phone Number field?
I would suggest that numbers should be allowed in this field, because it's possible, (although unlikely) that the user will have a number in their name and you don't want to penalise these people.
However, the counter argument is that if numbers have been entered it will probably have been done by mistake so the user should be alerted to this otherwise their user details for that transaction will be stored in error.
I imagine a compromise would be to alert the user ("Do you realise you've included numbers here, do you wish to proceed?") or similar, but from a straightforward - Should you validate against numbers in Name fields, Yes or No? which is the preferred option?