It may look black with your desktop printer depending on what you are using. 288 is a very dark, almost purple and it probably looks black when coming off of your printer. If you look at it with a loupe you will probably see some purple hues in there.

Are you getting this printed offset? Is it going on a coated or an uncoated substrate/paper? Is the paper you are using going to be white? Paper color makes a big difference.
Depending on how color critical your project is you may want to make some adjustments and up a number or two like maybe 286. Is your project, as a whole, 4 color and that is why you are building your pantone color out of process instead of using the PMS 288?

thanks for the tip, but i've triued the usual routes, and the really annoying thing is that its printed on another job fine (main client so about 40 times a week!) It sods law that the one job it did screw up on was a biggy (client wants a reptint) so money haggklesw aside (for now) we can't work out how it happened.
The printers saying theres defo a rogue RGB in there somwhere, do you think they've messed up and trying to cover their backs?

I won't go there, but-

If this is a repeated job, an (A) client and we know it is a "LOGO", then you should be running that PMS as a lone agent and not built out of 4 color. There are a lot of 5 and 6 color presses out there looking for work. When you build a pantone color out of process you are dealing with 4 ink densisities that the press person needs to match from run to run and that is difficult. It is almost setting the job up for failure. I don't have my conversion tables in front of me but I am pretty sure that 288 is made up of at least 3 of the 4 process colors. I could give you a list a mile long of variables that can cause inconsistent color on the press let alone in the file and RIP.
Building a pantone color out of process is not a good practice and a customer should be made aware from the beginning that you are going to get what you pay for because the only reason to do that in the offset printing world is to save money and it doesn't sound like you saved much.
I don't mean to be harsh or sound like an a** but it has always been a pet peeve of mine.
I say sell the customer on a 5 color job.

One thing I've learned. Just because you got the color to come out before, does not mean it's reproducable again. Over time, the RIPs, the Graphic Programs, the Firmware on the printers, the media, the humidity, etcc... change. And so with it, you find that you cannot reproduce something that was done just last month. Trust me. Heck, as I found out recently even a media size setting can get corrupted and screw up your tiling jobs. not pretty.

Ditto on what Cappy said. I looked on my solid to process swatchbook, and 288 definately suffers when converted to 4c process. It looks like a muddy almost denim blue instead of the brilliant royal blue the spot ink maintains.

Then again, it may be that your printer's trying to pull one over on you. You could ask to see their film & negs to prove it wasn't their fault.

Good luck!
-Jason

Thanks guys its still an ongoing problemo, though i'm convinced the printers trying to pull a swifty! He even sent the file to AGFA, though conveniently 2 weeks later still haven't heard anything! Thanks for all the advice though guys appreciated.
DannyBoy

truthfully I just looked at my pms swatches and would understand more if it was say a 296, or289 or even 282. Why? because he might have banding issues and is having it multistrike which lays out more ink, of course this only applies to large format printers.