Apparently, Expand has changed from a boolean Property to a Method.
Should be noted as breaking change in the Release Notes.

this.grid.MasterGridViewTemplate.Groups[i].Expand=true;

is now

this.grid.MasterGridViewTemplate.Groups[i].Expand();

Hello erwin,

You are correct. Thank you for reporting this. We moved its functionality to the Expand and Collapse methods of the DataGroup. You could use also the IsExpanded property of the GridViewGroupRowInfo. We will update our documentation shortly. I have added points to your account for the suggestions.

Do not hesitate to contact us, if you have any other questions.

Sincerely yours,
Jack
the Telerik team