Truecolor functions won't work after GD install

Hi, I'm running a Matrix dedicated server (based on Redhat) with PHP 4.2.2 installed as a shared module, phpinfo() reports GD 2 or greater installed (and rightly so, cos that's what I compiled!) and everything works fine apart from the following two functions: imagecreatetruecolor() and imagecopyresampled() Use of either of which simply causes the script to simply time out, no errors are reported to the server logs, the script just stalls whilst loading. Any ideas anyone, it's just that these are the two features I really needed! :( Thanks K