Wasps coach Shaun Edwards admits his side are massively disappointed to have been knocked out of the Heineken Cup at the group stages.
The 2004 and 2007 European champions failed to qualify for the quarter finals after defeat to Castres left them stranded on 17 points and in second place in Pool 2.
Edwards's men went into the fixture knowing a bonus point win would have guaranteed qualification for the last eight but a 21-15 defeat brought their campaign to a frustrating end.
"Obviously we are all very disappointed with the result and the fact that we are now out of the Heineken Cup," said Edwards, who had been a part of both Wasps' previous Heineken Cup triumphs.
"It was massively important for us to get to the quarter-finals."
Wasps led 15-14 at one stage but they failed to take their chances and were eventually made to pay by a Castres side that had also beaten Leinster at home earlier in the competition.
"The first try Castres scored, they picked up and almost walked over the line and for the last try, we were unlucky to have a man down in defence," added Edwards.
"We played some great rugby and (Dave) Walder made a lovely break late on, but the counter-attack resulted in a try.
"We had lots of chances to win this game but at this level you have got to be able to finish those chances and we didn't do that today.
"We always knew that Castres are very strong and were always going to be difficult opponents. Getting the bonus point win here would have been exceptional."
2009 is the second successive year in which Wasps have failed to reach the knock out stages and Edwards has already set his sights on ensuring his side have the opportunity to put that record straight this time next year.
"Now we need to put this result behind us and move on. We have to concentrate on making sure we qualify for the Heineken Cup next year."