Is your form submission method GET or POST? (If you didn't specify it, it will be GET).
On a GET, the form is submitted with the parameters in the query
string of the URL which has limited space. You are probably over-running this limit when a lot of check-boxes are selected.
Be sure that you have
on your form declaration.
hth,
bear
[ April 03, 2003: Message edited by: Bear Bibeault ]