Help with exception error

Here is the whole list of errors after uninstalling Acrobat Pro DC 32-bit and installing 64-bit. I even tried doing a repair on the new install which is latest version:

Exception in line 1282 of function AFSimple_Calculate, script byteCodeTool
Exception in line 1 of function top_level, script Field:Calculate
Exception in line 1282 of function AFSimple_Calculate, script byteCodeTool
Exception in line 1 of function top_level, script Field:Calculate

TypeError: f is null
1282:byteCodeToolException in line 1282 of function AFSimple_Calculate, script byteCodeTool
Exception in line 1 of function top_level, script Field:Calculate

TypeError: f is null
1282:byteCodeTool

I thought the reset button was causing the issue, after I changed some of the code, but when I went back to original code

// A MouseUp action

var nButton1 = app.alert({

cTitle: "CLEAR FORM WARNING",

cMsg: "STOP! DO NOT CLEAR THIS FORM UNLESS YOU SAVE IT FIRST. \r\rIf you have not saved this document yet, go ahead and click NO to save now, otherwise click YES to clear this form. \r\rWould you like to proceed and clear this form now?",

nIcon: 1, nType: 2

});

//if user clicks on YES button it will alert the user that it will reset and ask YES or NO to proceed

if ( nButton1 == 4 ) {

// clear and reset all the fields objects in this document

this.resetForm();
} 

, still getting the error and also f is null error:

As for the rest of your question, it seems to be the location dropdown that is failing, but I have this code in the Service Heading field validation:

event.target.required = event.value == "--- Please Select One ---" ? true : false;

Maybe I'm not handling the validation correctly?

The code for the Location dropdown is:

if (event.value) {
var f = event.target;
var found = false;
for (var i=0; i<f.numItems; i++) {
if (f.getItemAt(i, false)==event.value) {found = true; break;}
}
if (!found) {
f.insertItemAt({nIdx: -1, cName: event.value});
f.defaultValue = f.getItemAt(0, false);
}
}

This is also on the validation tab.

On the Action script:

// Display alert box
app.alert({cMsg:"Please choose an Existing Location or enter a New Location (the new location will be saved in the dropdown list).",
cTitle:"Location Information Request",
nIcon:3,
});