I have worpdress 3.8.1. sometimes when i try to upload image, pdf using worpdress functions it gets stuck at 100% and nothing gets logged in the log files so i d onot know what the problem is. however I have seen the following which appear randomly, picture attached
cannot upload anything into wordpress
i have found the culprit.
http-authenticationplugin. not sure what it does but it was enabled and ticked as active, so i just unticked it.