This error seems to be cropping up more and more, based on influx of e-mails. So far, I’ve only seen it from users of OS X 10.7.4.
This error is a result of Apple’s sandbox not properly giving GIF Brewery permission to read your video file. I’m currently waiting for feedback from Apple as to what the best course is to resolve this issue.
As a temporary workaround to this error, you can put the video file on a USB drive and open the video from there. If this does not work, please contact via e-mail.
Technical explanation: GIF Brewery uses Apple’s Sandbox with the “read & write user-selected files” entitlement. Apple’s Quicktime framework needs more than this for some reason. I have a fix that gives a temporary entitlement to GIF Brewery, which allows complete read access to a user’s ~/Desktop, ~/Downloads, and ~/Movies folder — since these are the most likely place for video files to be.
This fixes the issue, however, it goes against the goal of Apple’s sandbox. However, it must be approved by Apple first and I don’t want to waste time in the App Store queue only to hear it will be rejected, so I’ve contacted Apple through their Technical Support Inquiry process first before submitting it to the store.