I am using a Hybrid Child Theme, which I have modified to fit my needs. Not only can I not upload media at all (it simply says "Error Uploading Media File"), but my Pages and Posts editors offer no options for adding photos, either. I do not have this problem with my other website, which uses version 3.3.1.
I have deactivated all my plugins and it has not resolved the problem. I really do not want to rebuild my entire site on the Twenty Tweleve theme, which seems to be the only theme that is working properly with the new version of wordpress.
Can someone please help me?