Php – Strange GD error when working on PNG images from PHP on FreeBSD

I have a problem with my FreeBSD 7.1 server. PHP's GD implementation no longer works on PNG images. Whenever the system tries to work with PNG images, I get these three error messages:

[Sat Jul 18 21:41:15 2009] [error] [client 90.34.34.34] PHP Warning:  imagecreatefrompng() [function.imagecreatefrompng]: gd-png:  fatal libpng error: [00][00][00][00]: unknown critical chunk in /usr/storage/www/private/mikkel.hoegh.org/modules/acquia/imageapi/imageapi_gd.module on line 44, referer: http://mikkel.hoegh.org/admin/build/imagecache/3
[Sat Jul 18 21:41:15 2009] [error] [client 90.34.34.34] PHP Warning:  imagecreatefrompng() [function.imagecreatefrompng]: gd-png error: setjmp returns error condition in /usr/storage/www/private/mikkel.hoegh.org/modules/acquia/imageapi/imageapi_gd.module on line 44, referer: http://mikkel.hoegh.org/admin/build/imagecache/3
[Sat Jul 18 21:41:15 2009] [error] [client 90.34.34.34] PHP Warning:  imagecreatefrompng() [function.imagecreatefrompng]: 'sites/mikkel.hoegh.org/files/imagecache_sample.png' is not a valid PNG file in /usr/storage/www/private/mikkel.hoegh.org/modules/acquia/imageapi/imageapi_gd.module on line 44, referer: http://mikkel.hoegh.org/admin/build/imagecache/3

I've been trying to solve this half a day now, and the best clue I've found is another guy having the same problem – no solution there, though.

The code in question is fairly simple, it just calls imagecreatefrompng($filename);

Package versions of all the packages I can think of that might be related:

• php5-5.2.10
• php5-gd-5.2.10
• png-1.2.37
• gd-2.0.35_1,1

Any clues?