I have a WebGrid that breaks in javascript when refreshing after updating data. The grid is complex, withgrouping at the top level and two levels of child table, and it is full, with 424, 1389 and 7116 records at the three levels of the hierarchy.  The break does not occur when the volume of data is low, like 7, 30 and 904 records.

The grid loads ok initially, and when refreshing the grid after a data update, there is no problem while the progress message "Refreshing data..." shows.  But then during "Loading group..." the client breaks with the exception:

Unhandled exception at line 1, column 104896 in http://localhost/ISRes.axd?G/WebGrid_UI.js/807200259

0x800a138f - JavaScript runtime error: Unable to get property 'fullPath' of undefined or null reference

The break is on p.fullPath where p is null in:

ResponseLoadGroup:function(c,q){var a=ISXml.GetNodeText(q,"//htmlString");var k=c.Tables[ISXml.GetNodeText(q,"//tblName")];var l=k.GetElement(WG40.BODY,WG40.HTMLTABLE);var p=c.LastRequestObj;var f=p.fullPath;

Is this a known problem, and is there a workaround (other than reducing the volume of data)?