Some thumbnails are not being created by ImageMagick

I am using Omeka 2.3 on a centos server with ImageMagick 6.7.1. I am having troubles when uploading some images, but not others. The error log tells me that ImageMagick is having troubles creating thumbnails. Error code is:
ImageMagick failed with status code 11
I checked if all the failed images have something in common, but I could not find anything. They are of different types (jpg, png, gif) and have very different sizes, both in terms of total size and dimensions. I could not get information about the status code, so I am hoping you guys can help. Thank you.

If you control the server, the first thing I'd try is updating ImageMagick, either from a newer version from the CentOS repos you're using, if one is available, or using the RPM available directly from ImageMagick on their website.

Thanks for responding so fast. Unfortunately, updating ImageMagick is not so easy as the new version is not available from CentOS repos. I would have to deinstall and reinstall the new version of ImageMagick. I am not sure if I want to do that, because I am worried this might create even more problems. Is there anything else I could try?