UBB.threads PHP Forum Software Community Forums UBB.threads 7 Installation and Upgrade Support Captcha image missing

Hi,

For some reason Captcha has stopped displaying images during the registration process on my site? I've checked the forum permissions and everything checks out as okay. When I run the captcha test that Rick suggested 5 posts above (ubbthreads.php?ubb=captcha&t=im&test=1), I get the following error:

PHP error: convert: unable to read font `/usr/www/users/iwrf/forums/images/captcha/fonts/_vti_cnf' @ annotate.c/RenderType/1075.

If I refresh the page I get this error:

PHP error: convert: missing an image filename `GIF:/usr/www/users/iwrf/forums/cache/03995596e1f846ffdeb0fbe94aec60a0.gif' @ convert.c/ConvertImageCommand/2775.

I'm not sure what has happened as everything was working fine a week ago, and I haven't changed any settings before then or since. Does anyone have any suggestions on what I can try to get captcha working again so people can register on my forum again??

Many thanks in advance!!
www.iwrf.com/forums/