You would have added the error code as per Jason's instructions back in post #4, necessary to troubleshoot your original problem. The error code is not in the page by default but is a useful bit of code that can be added to the beginning of a page to allow the errors to be printed to the screen so that a diagnosis can be made. It just happened that on this occasion, an extra space managed to wiggle its way in there.
You can change the properties of the captcha image to make it more readable, or to better suit your site style by making alterations to your wavt_captchasecurityimages.php file (again).
The line that would probably be best to change for readability (?) would be the noise colour one which (on your page) would be somewhere near line 178:
$noisecolor = isset($_GET['noisecolor']) && $_GET['noisecolor'] != "" ? $_GET['noisecolor'] : '000000';
If you change the noise color from '000000' to something like '999999', i.e:
$noisecolor = isset($_GET['noisecolor']) && $_GET['noisecolor'] != "" ? $_GET['noisecolor'] : '999999';
it would make it easier to see.
(000000 is black, 333333 is dark grey, 666666 is medium grey, 999999 is light grey and CCCCCC is even lighter grey) The idea being to get just enough contrast for a human to read and for OCR (character recognition) software to get a headache.