#2 GD Error

[Anonymous]

Error Log shows...
gd-png: fatal libpng error: zlib error
gd-png error: setjmp returns error condition

The guestbook doesn't show the Captcha code so security check during sign-up can't be made.

Server Apache2.2
PHP Version 5.2.5
MySQL 5.0.45-community-log

GD etc are working fine with other software packages just this guestbook having issues

[Nobody/Anonymous]

in "gbook.php"
row 512 and 935
replace
if (extension_loaded("gd"))
with
if (extension_loaded("gd2"))