object undefined instead of string literal

I wrote a piece of code that allows me to pass a numeric primary key for update when looping through a recordset. This works fine, however, I am doing the same routine for one level deeper into the database structure and the primary key is concantenated and the component I need to pass is a single leter. The code that works so well with the number, now dies and gives the 'object undefined' error...I just want it to pass a string literal...
Any help is apprecited. here is the code for the function:

jsProdPayType = "";
jsProdNm = "";

function setProdPayTyp(num){
jsProdPayType = num;

}

here is the function call : this is in a jasp file.

<td><input type="radio" name ="select_record"  onclick="Javascript:setProdPayType(<%=rs_row.elementAt(3)%>);" > </td>

again, this works fine when i am passing a number... but I now need to pass an alpha char as the key ....