IE 5.5 not performing comparison correctly

I am using PHP 4.2.3 with Apache 1.3..11 on Windows 2000 Pro. I have a form that POSTs a variable to the next page. PHP code at the top of the second page checks the POST variable against values in a flat file. If the POST variable and one of the values in the file match, the code breaks out of the if and sets another variable to a value. When I look at the page with Netscape 6, it works like a champ. It does not work in IE 5.5. I have verified that there is no whitespace around the variable from the POST or the file. I have also verified that the variables are of the same type. Has anyone seen this before? How did you fix it? Giff