FMP 7 - Validate Fields

I have successfully used Instant Web Publishing to get a database on the web.

What I need to happen is for users to be able to enter/update values in

certain fields Depending On The Layout. Using a validation based on a

calculated value, I got it to work OFFline. If the user enters something into a

field on an incorrect layout, when they go to leave that record, a custom

validation message appears telling them they can't change the value and they

must revert to the previous value. When I try the same thing on the web, no

error message appears, the current page looks like it is reloading and I

cannot exit the file. When I try to exit the original file, I get a message that

someone is still connected, but I cannot kick them off. I must force quit

FileMaker.

Does anyone either know what might be the problem OR have ideas for how I

might stop web users from entering values into certain fields only if they are

on certain layouts?

Thank you for your help,

Nancy