>>Maybe it has something to do with Time Zones?
>
>Ok, here's our test results.
>
>So far, we have isolated the problem for someone using a time zone other that the one on our server. Even is the server local time and the user local time is for the same day, when the user is sending the DATE() value, it is set to DATE()-1. That only occurs for users having a different time zone that ours.

Maybe you should decalre date parameters as string parameters and than convert them to date on your end?