I just downgraded an AP and an SM to 2.3 and then upgraded to 2.3.3 with executables that I got off of the web site. It worked for me. Could you try downgrading again and let me know if there was any improvement. The error sounds to me like there was something wrong with the download.
Getting same error message...i redownloaded and used a differnet browswer (safari / chrome) still the same error...this was not happening before... It was happening with 2.3.1 as well but i dnd' post anything since i noticed from the comunity that 2.3.1 had issues.
the instruction for upgrade on the release notes PDF says that the file extention is .tar.gz and when i download it it only gives me .tar extention.