I also have this problem (ERROR HTTP error. : HTTP Error. occuring when trying to upload images to the NextGen gallery) and it seems to have broken the moment I updated Contact Form 7. Temporarily disabling the Contact Form 7 plugin allows me to upload without any problems – so it definitely seems to be that plugin in my case – thanks for pointing me in the right direction!
Let’s hope they put out a fix for this – both those plugins are very popular so surely it’s affecting a lot of people.
