Limits

Hi people, is there a limit to the number of fields that can be updated in a mysql database at one time? ie can we update as many field with the one query as we like, or is there a maximum number of fields that can be changed.? The reason that I ask is that I have a large number of fields that need to be entered into a database on a form submit that I have decided to split over a few pages. The first page submits the data into the database no problem, the second page uses an update query and that works, but from then on the following 3 or 4 pages do not update the database with the data entered. Any ideas as to why this would be happening, I've done this before and never had the trouble, however this time I do have a lot of fields in the d'base and each query is quite large itself. Kind regards, Shannon