Calculating age from DOB field in Acrobat

This is a followup to Calculating Age from DOB field in Acrobat  but I'm opening a new question because every time I respond to an existing question in various techs support forums I get slammed. If opening a new question is the wrong thing to to here, I apologize.

Using Acrobat X, I am trying to use this code in a field named Age to calculate age from a field named DOB (I'm sorry but I don't see an editing button to format it as code):

event.value = "";

var dobValue = this.getField("DOB").value;

if (dobValue!="") {

var dob = util.scand("dd/mm/yyyy", dobValue);

var today = new Date();

// compute age in milliseconds

var age = today.getTime() - dob.getTime();

// convert age to years ( millsec in sec * sec in min * min in hrs * hrs in day * days in year)

// truncate to whole years and adjust for binary floating point error

event.value = Math.floor( age / (1000 * 60 * 60 * 24 * 365.2425) - 0.005);

}

The debugger throws the following errors. How can I fix these?

dob is null

11:AcroForm:Age:Calculate

TypeError: dob is null

11:AcroForm:Age:Calculate

The DOB field is formatted as Date m/d/yyyy, and there very definitely is a value entered in that field.

Thanks to all.