Hi I am having a similar problem. Using firefox 3 (on mac) the example page loading with json. There is just nothing loading. Firebug show on line

jqgrid.base.js # 626

row.id = cur[idn] || cur[ts.p.jsonReader.cell][idn] || i+1;

cur[ts.p.json.Reader.cell] is undefined.

Which file you add that line and fix it?