UPDATE: See first comment. Reuters says
The state's House of Representatives objected to language in the bill [added at the insistence of the governor] that would have allowed religious groups to decline to participate in same-sex marriage ceremonies or to offer gay couples other services.
A handful of gay-rights proponents sided with Republicans in the Democratic-controlled House to vote down the bill....
The Boston Herald adds:
Among the onlookers was Episcopal Bishop Gene Robinson, the first openly gay bishop in the church. He said the House pushed the pause button, not reverse, and is optimistic lawmakers will come up with an acceptable bill this session.
The New Hampshire Senate passed it, the governor was standing by to sign it, and many expected approval of a final same-sex marriage bill in the House today could be swift and routine.
But in a surprise turnabout, the New Hampshire House voted narrowly Wednesday afternoon to defeat the measure, 186 to 188.
When the House Speaker announced the vote in the House, the chamber erupted with sounds of both distress and applause. Supporters and opponents then launched immediate efforts to both save and kill the measure for this legislative session.