PHP and Windows - problem with php_mysqli.dll

I'm trying to get a mysql driven site working, but have hit a nasty problem Started off with php 5 but that simply refuses to find the dll. rolled back to 4.2 or some such, which then fails to load when the dll is included in the extensions list. So long as mysqli line is commented out, its fine. There is definately one copy only of the dll on the server. using w2k3, mysql 5 * * * * * * * * * * * * Help protect the environment - please don't print this email unless you really need to. * * * * * * * * * * * * This communication is from City of York Council. The information contained within, and in any attachment(s), is confidential and legally privileged. It is for the exclusive use of the intended recipient(s). If you are not the intended recipient(s), please note that any form of distribution, copying or use of this communication, or the information within, is strictly prohibited and may be unlawful. Equally, you must not disclose all, or part, of its contents to any other person. If you have received this communication in error, please return it immediately to the sender, then delete and destroy any copies of it. City of York Council disclaims any liability for action taken in reliance on the content of this communication.