How to you troubleshoot the error "the value entered does not match the format of the field"?

No, just sums.  See example below.  Field1 is a text field with a value of "." or "yes".  Fields 2, 3, and 4 are total fields of numbers.  The *1 is being used to get the formatting needed of the number without decimal places. 

var a=this.getField("field1");

var b=this.getField("field2");

var c=this.getField("field3");

var d=this.getField("field4");

if (a.value=="yes"){event.value=''}

else

event.value=b.value+c.value+d.value*1;

if (event.value==0||event.value=='') {event.value=''};