It's a reluctant welcome back to the Robin Williams of gurning schmaltz, apple-pie values and saccharine world view for this sputtering comedy vehicle.

Entertainingly playing against (this sort of) type in Insomnia and One Hour Photo had seemed to suit the actor as age caught up with him... but here he's simply regressed.

He plays Bob Munro, a stressed-out executive threatened by younger, more aggressive upstarts at a Coca Cola-style soft drinks company.

When he falls out with his slimy boss big-time, he's called in to rescue his career at a tricky takeover meeting with a small beer firm in Colorado.

The trouble is he's promised to take his family - spiky wife Jamie (Hines), brooding teenage brat Cassie (JoJo Levesque) and self-conscious son Carl (Josh Hutcherson) - on a break to Hawaii.

Pitching a trip of familial togetherness but secretly planning to make the crunch talks, Bob persuades them to take an RV holiday alongside other caravanners even if - as his wife points out - his white-collar brood "don't do friendly".

It doesn't help that the RV concept - eight million American households annually manouevre the bungalows-on-wheels to 8,500 RV parks a year - doesn't compute to the average British viewer.

The closest cousin to the luxury RV is a tin static caravan you might spot gracing a field outside Tenby and the common US conception is that it's the sort of break taken by stateside chavs.

So Bob and co immediately run into Jeff Daniels' family of redneck misfits - his pneumatic "cosmologist" wife and their slightly crazy kids. Cue mirth as the Munros can't seem to shake off their well-meaning but uncouth new chums.

There's the almost obligatory setpiece involving human waste (you search in vain for Armitage Shanks' co-producing credit) and the dysfunctional Munros eventually bond in fit of giggles at the foot of a mudchute. It's that kind of movie.

Despite some sharp lines from Daddy Day Care scriptwriter Geoff Rodkey and Barry 'Get Shorty' Sonnenfeld at the wheel, this never really gets out of first gear and suggests the most interesting new stage of Williams' career is over.

One comedy breakdown even the AA won't take calls for.

Tim Evans