If using ExtJS 3.3.0, and LovCombo, then you will need to make the following modification to Ext.ux.grid.RecordForm.js:

On line 300, replace this:
Code:
            // use cm editor if we have one
            if(c && c.editor && c.editor.field) {
With this:

Code:
            // use cm editor if we have one
            if(c && c.editor ) {
                
                c.editor.field = c.editor;
Worked for me
Thanks for such a useful plugin, it's a big timesaver when I just want a simple editor of a simple record.