HTTP Error while uploading

Today, I began receiving HTTP errors when trying to upload images. It doesn’t finish crunching and nothing happens. This has never happened to me before, and I’ve been working on this community blog for 3 years. We changed themes two weeks ago, but haven’t experienced any problems until just now.

Additionally, I’d like to also point out that I’ve inherited the blog from our old webmaster last fall–it’s a college group organization blog–and he didn’t give me any information about the technical fundamentals of WordPress. So people mention htaccess on the internet, but I really have no idea where that is to be found and I certainly don’t have it located anywhere on my computer/I haven’t downloaded anything.

Also, this website was created several years ago and I have a weird suspicion/feeling that it was created before the WordPress.com/Wordpress.org separation and am not sure what that means for how I’m supposed to fix this problem.

So, with those notes, please help!