Server switch - SEF Advance weirdness

Hi, I've just transferred my client's site to a new dedicated server. Their mambo site appears to be working just fine apart from a few links.
Each URL output by menus now has an "&Itemid=xxx" parameter tagged onto the end. So what was:

/LinuxIT_professional_services/technical_support/SuSE_Linux_Support/

is now:

/LinuxIT_professional_services/technical_support/SuSE_Linux_Support/&Itemid=240

This is provoking 404 errors on section and category index pages. Strangely content items continue to work fine despite the extra itemID parameter.

I'd greatly appreciate some help in sorting this out.

Thanks.

Al