customer email field is grayed out at random times

I have a client that has HQ and 2 stores and when a clerk enters a new customer the the email field is "greyed out", but other fields are fine. This happens at random times. They can create new customers all day and then all sudden the email field is greyed out for one customer, but the next new customer is fine. I checked the security level settings and their is none set. I recently deleted duplicate customers using a script I got from MS tech support and I not sure that could of cause the problem. Thank you for your support Thanks Dave