Williams says it feels "embarrassing" to have been the only team to have missed the start of testing with its new Formula 1 car.
Deputy team principal Claire Williams said the team only became aware of the trouble it was in last weekend, although it has declined to elaborate on exactly what went wrong.
"This is not a situation we anticipated," said Williams, speaking at the Barcelona test on Wednesday afternoon. "It's not a situation we ever wanted to find ourselves in.
"We're not just disappointed but it's embarrassing not bringing a race car to a circuit when everyone else has managed to do that.
"Particularly for a team like ours that has managed to deliver a race car to testing for the past 40-odd years. So we can only apologise."
While the team will run an analysis to get to the bottom of what happened, Williams said that the focus for now was just on getting its car running and try to minimise the disruption to its pre-season programme.
"It became apparent quite late on actually, that we weren't going to make the shakedown and subsequently not make the first day," added Williams.
"We thought we could get everything we needed together in order to make Tuesday. And then parts just weren't coming through as we hoped they would, and in the time we hoped they would or had in the plan. So we didn't make it until today.
"But I'm not going to go into any detail as to why that happened. I don't think it's appropriate to discuss the ins and outs of what went wrong. Completing that inquest anyway has not happened at Grove yet.
"We're clearly aware of some of the issues but it's too early to start discussing them in any detail and probably something we wouldn't do anyway. We need to resolve what went wrong so this doesn't happen again at Williams."
The difficulties that Williams has faced have prompted questions about the future of its technical chief Paddy Lowe. Williams herself refused to comment on the situation.
"I've been reading a lot of speculation in the media recently about Paddy's position," she said. "Right now all I'm focused on, and all the team should be focused on is the car, and making sure the car is in the right place."
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- Formula 1