[RESOLVED] Error when sorting data with formula

i'm passing a boolean to CR in vb.net
and then want to sort on either first name or surname depending on what value is passed.

ive set the sort order of the records to be the name of my formula, and then in my formula put this code:

VB Code:

if {?@boolVal} = True then
   {first_name}
 else 
   {surname}

problem is that i get an error saying that
Error in formula . ' if {?@boolVal} = True then ' This field name is not known.


any ideas??

ta