parsing "^[([a-z]|[A-Z])[.]([a-z]|[A-Z])]{1,25}$" - Too many )'s

What is wrong with my expression that I get the above mentioned error. It occurred at this code:

if ((!Regex.IsMatch(x, @"^[([a-z]|[A-Z])[.]([a-z]|[A-Z])]{1,25}$"))