Unable to upload PNG images I'm running Craft CMS on OS X Yosemite (Server.app) and cannot upload PNG images. JPG uploads are working as expected. I get a log message like the following:

2015/01/15 08:39:08 [error] [exception.Imagine\Exception\RuntimeException] exception 'Imagine\Exception\RuntimeException' with message 'Unable to open image .../craft/storage/runtime/temp/assets54b77cabe51c25.46473389.png' in .../craft/app/vendor/imagine/imagine/lib/Imagine/Gd/Imagine.php:96
Stack trace:
#0 /*/craft/app/etc/io/Image.php(136): Imagine\Gd\Imagine-&gt;open('...')
#1 /*/craft/app/services/ImagesService.php(84): Craft\Image-&gt;loadImage('...')
#2 /*/craft/app/services/ImagesService.php(153): Craft\ImagesService-&gt;loadImage('...')
#3 /*/craft/app/assetsourcetypes/BaseAssetSourceType.php(183): Craft\ImagesService-&gt;cleanImage('...')
#4 /*/craft/app/assetsourcetypes/BaseAssetSourceType.php(145): Craft\BaseAssetSourceType-&gt;insertFileByPath('...', Object(Craft\AssetFolderModel), 'HSS_Highlife_20...')
#5 /*/craft/app/services/AssetsService.php(673): Craft\BaseAssetSourceType-&gt;uploadFile(Object(Craft\AssetFolderModel))
#6 /*/craft/app/controllers/AssetsController.php(71): Craft\AssetsService-&gt;uploadFile('1', NULL, 0, NULL)
#7 /*/craft/app/framework/web/actions/CInlineAction.php(49): Craft\AssetsController-&gt;actionUploadFile()
#8 /*/craft/app/framework/web/CController.php(308): CInlineAction-&gt;runWithParams(Array)
#9 /*/craft/app/framework/web/CController.php(286): CController-&gt;runAction(Object(CInlineAction))
#10 /*/craft/app/framework/web/CController.php(265): CController-&gt;runActionWithFilters(Object(CInlineAction), Array)
#11 /*/craft/app/framework/web/CWebApplication.php(282): CController-&gt;run('uploadFile')
#12 /*/craft/app/etc/web/WebApp.php(754): CWebApplication-&gt;runController('assets/uploadFi...')
#13 /*/craft/app/etc/web/WebApp.php(261): Craft\WebApp-&gt;_processActionRequest()
#14 /*/craft/app/framework/base/CApplication.php(180): Craft\WebApp-&gt;processRequest()
#15 /*/craft/app/index.php(62): CApplication-&gt;run()
#16 /*/public/index.php(14): require_once('...')
#17 {main}
REQUEST_URI=/index.php?p=admin/actions/assets/uploadFile
HTTP_REFERER=http://*/index.php?p=admin/entries/banners/5-highlife-vanguard
---
2015/01/15 08:39:08 [error] [application] Unable to open image craft/storage/runtime/temp/assets54b77cabe51c25.46473389.png


It looks like a problem with the Imagine library not being able to open the uploaded PNGs?
Is there anything special about that PNG file?  It's likely that it's in a PNG format that GD does not support.

Install Imagick and try again.  It handles a much wider range of formats, is generally less buggy and produces better results.  Craft will automatically use it if it detects that it is installed and available to PHP.