Calculation/Validation/Action

I'm kind of stuck or missing something here. I have a DropDown with 3 entries preformatted but also have the option check to let users enter custom text. However thats not ths issue. 

The issue is that no matter if i put a script in the "Actions" tab under mouse up run JavaScript, or in the validation script or the calculation script i am getting an error : "InvalidSetError: Set not possible, invalid or unknown."

and when selecting a name in this dropdown it does not execute the code to put a time in the var b field.

Here is the script and error from my console window.

var a = this.getField("ddName");
var b = this.getField("StartTime");


if (a.value = "Name1"){
b.value = "7:30am";
}
else if (a.value = "Name2"){
b.value = "8:00am";
}
else if (a.value = "Name3"){
b.value = "10:00am";
}
else
b.value = ""




Exception in line 4 of function top_level, script AcroForm:ddName:Validate


InvalidSetError: Set not possible, invalid or unknown.
Field.value:4:AcroForm:ddName:Validate