Northampton Saints head coach Jim Mallinder has admitted that "basic mistakes" cost his side during Friday's defeat to Castres in the Heineken Cup.
The visitors were unable to build on last weekend's victory over Glasgow Warriors as they went down 21-16 in France.
"We came up against a good side tonight on their own patch and knew it would be tough, just like it was last season," Mallinder told Sky Sports News. "We fought well, but basic mistakes ultimately cost us the game.
"We must now look forward to Ulster, which will again be another tough game, but we've been in good form this season, and we know we can get a result against them at our place."
Northampton return to Aviva Premiership action next Saturday when they host Saracens at Franklin's Gardens.
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