A contrite Claire Williams has faced the F1 media in Barcelona, admitting Williams' absence from the opening two days amid fierce speculation was "embarrassing".
But the once-great British team's deputy boss would not comment on precisely what the problem was back at the Grove factory.
"It wasn't just one thing," she told Finland's MTV, "but I'm not going to talk about it publicly.
"We need to focus all of our energy on this test."
Williams' delayed FW42 finally got up and running on Wednesday, some 8 seconds off the leading pace.
Many have observed that Williams' simple livery and car design, coupled with the Barcelona delay, hint at obvious money problems.
"No, it has nothing to do with money," Claire Williams insisted. "It's about not getting the car ready on time.
"First we wanted to do a shakedown and we found that we couldn't. The parts just did not match as we expected," she said.
"But I'm not going to go into any details about why this happened. We still need to analyse it and ensure that it doesn't happen again.
"There is no excuse. All the other teams finished their cars on time, and we did that as well for over 40 years. It is embarrassing that we are so late.
"I can only apologise to all the fans and to our drivers. We are all extremely disappointed," Williams added.
She said the team now has to "live with compromises" ahead of the 2019 season, just as Williams desperately needs to pull itself off the back of the grid.
But she rejected rumours Williams might not be able to race in Australia with two cars.
"I can guarantee that we will have not only two cars in Australia but a spare chassis and enough spare parts," she said.
"It would be an understatement to say that the last days have been terrible for us, but finally we have the car on track and we can start working."
One big rumour during the delay is that technical boss Paddy Lowe could be sacked. Lowe's media duties for the entire Barcelona test have been cancelled.
"I did not pay much attention to all the speculation," Williams said, "but we are not going to waste energy with blame or washing dirty laundry in public."
As for Lowe, Claire said he will "concentrate his energy on getting our car in the best possible condition" rather than taking difficult questions from the media.
