Grouping in excel using matlab actxserver gives invoke error

When I use the command below, I get the invoke error. Any idea how I can get rid of this error?

I was trying to group these rows, and Excel did grouped them, but I get the error anyway....

>> set(sheet1.Range('12:18'),'Group',1);
??? Invoke Error, Dispatch Exception:
Source: Microsoft Excel
Description: Unable to set the Group property of the Range class
Help File: xlmain11.chm
Help Context ID: 0