Success! Looks like we've fixed this one. According to our records the fix was applied for
a bug in our system
a recent build.
[4.0.2] groupToggleMenuItem is null
When using 'Ext.grid.feature.Grouping' with 'enableGroupingMenu: false' config parameter there is an error in ext-all-debug.js at line 79141 when toggling grouping feature enable/disable. The error 'groupToggleMenuItem is null' is at line:
So, you just need to add a check for 'groupToggleMenuItem is not null' to resolve this.