1. treeGrid:true, datatype:'jsonstring' ('jsonstring' is a documented requirement for treeGrid).

2. When you do 'GetGridParam', the 'datatype' has been set back to 'local' somewhere inside jqGrid.

3. This causes the attempt to create the new version of the grid to fail.

Solution: 

var ccm = $("#treegrid").getGridParam();

// force datatype back to what we originally set it to, and what treeGrid needs

ccm.datatype = 'jsonstring';

$("#treegrid").jqGrid("GridUnload");

$("#treegrid").jqGrid(ccm);

I could send a complete example if you want.

I'm still working on the hideCol one … I'm pretty sure it's specific to treeGrid, though, and this explains why your demo works. Of course, one would hope that hideCol works in the treeGrid as well.

On a related note, do you agree that this code (below) should always work, assuming '#treegrid' starts off as a normal, successfully rendered, 'working' grid?

var ccm = $("#treegrid").getGridParam();

$("#treegrid").jqGrid("GridUnload");

$("#treegrid").jqGrid(ccm);

It yields a GC error, "Uncaught TypeError: Cannot read property 'stype' of undefined". I will isolate this as well, if it would be useful to you.

We need a test case. There is no error if we use the demo here

http://trirand.com/blog/jqgrid.....qgrid.html

New in version 3.2 => Hide/Show columns

Regards

$("#mygrid").jqGrid("hideCol",col_name);

Yields this (in GC):

Uncaught TypeError: Cannot read property 'width' of undefined

The hide works (eg. the column disappears), so col_name must be OK, and the grid is otherwise working fine.

Any advice?