filter by form email address problem

I have a form displaying contact details. One of the fields being email address. Works fine until I enter an email address to search for with a "." before the "@". So

It will search for

kenjones@

But

ken.jones@

Will generate the following error

"The expression you entered contains invalid syntax
You may have entered an operand without an operator"

I did think that this would be a really common problem and the net would be awash with fixes. Cant find anything though. Any ideas?

Can you show the query or filter that you are using?

I'm using the filter by form buttons at the top of the page. When you press the first [left hand] one you are presented with the form cleared so you can enter what you want to search for in one or more of the boxes/fields on the form. When you press the second [RH] button it runs the filter and returns the results that match. Or dosen't if there is a pesky "." before the "@"!!!