It depends on what you're attempting to do. It's not insufficient in law to create a legal obligation to attend, but it may be insufficient to go out and have someone arrested for not attending. You may need an order of the House, a Speaker's warrant, which in effect directs that the person be forcibly apprehended and brought here. But short of that, the summons is legally effective to cause someone to be legally obliged to attend before the committee.
On November 27th, 2007. See this statement in context.