I am stuck between a rock and hard place with this and one of my clients.
It's a long one so please keep reading

We sold this client a pretty standard computer network setup about a year ago.
They got 4 HP workstations and an HP SBS2003 entry level server.
They have a FujiXerox colour digital copier/printer/scanner.
They also got a Micronet ADSL2+ router for the internet connection.
They have been happy and everything has been working great since and we have had a great ongoing relationship.
Then, I have no idea how, they got sold a managed hosted service.
Out of the blue I get a call from the client saying I need to go onsite, install some updates that are required for this hosted service (.NET 3.5SP1, RDP client and XP presentation manager patch were the main ones) and backup all their data from the sbs2003 box so that they can courier it to the hosted service provider to be loaded onto their servers.
That's all fine and was done without a problem.
Then a week or so later I get a call from the service provider saying this client is having some issues and can I please go and sort it out for them. I thought this was a bit odd straight away as it wasn't us that sold them the hosted service so why should we fix their problems with it? Surely that should be part of the service they are paying for from the hosted service provider?
Anyway, they said they suspect that it is a printer driver problem and could I please go and change the driver to a PCL driver.
So I went and did this and found that they were already using a PCL6 driver but not the latest WHQL version so I removed the old one and installed the latest one. This however did not fix the problem. I have since tried 4-5 other drivers supplied by FujiXerox that have not fixed the problem.
The actual problem they are having is with some of their Excel spreadsheets.
They change the view to page break view and then adjust the page breaks manually to the area they want to print and this has always worked on the local systems.
When they try to do this on the hosted service it freezes of a few seconds then all of a sudden every cell has a page break around it. Using Undo doesn't get rid of them.
I tested and confirmed that the problem is the printer driver because logging in to the hosted service, without the fujixerox driver installed, Excel works fine.
The hosted service provider also tested from their end with an HP printer and it is also fine.
The hosted service provider is now saying that there is nothing wrong with their system and the problem lies with the printer driver or the physical setup at the clients site.
They have also spoken to another "specialist" who is of the same opinion as them.
I did some more testing on site today by logging in to our own 2003 terminal server, installed their printer driver (as you have to do with the 2003 TS), transfered over a couple of the excel spreadsheets that they are having problems with and they worked fine.
So now this is where I am stuck and don't know what to do next.
The hosted service provider is basically blaming us for the client's physical setup onsite or the printer driver.
I have proven that there is nothing wrong with the client's physical setup as everything works great on the local machines and has done for about a year.
I have also proven that their printer driver works in a 2003 terminal server environment, granted this is not the same as 2008, which I don't have access to easily.
Anyone have any ideas, thoughts?
What I should do next?