Thank you...
Yes were on the right track...
I have a custom php file in my forums directory which through a template is being included, all that php file really has in it is that function, the template is not being saved telling me it's undefined...
So in the php file I've included the line : $safe_functions[] = 'myFunction';
but it's a no show still...
It all used to work

using vBulletin 3.8.7 Patch Level 4 - Just need to let vB know that myFunction is a good'un and I'm golden.. the custom php file is being included, just can't save the template without an error....
Thanks for the help.
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EDIT, I'm getting it now I think....