I\'m running WP 3.0.1 on a shared host using PHP5. I\'m having issues uploading files that are a little larger via the media uploader in the admin section of WP.
Eve
The problem, as you've already inferred, is in the size of your file upload. Just to remind you, HTTP isn't really built for transferring large files ... it can do it, but not always, and not very well. You're running into an issue where your host is cutting off the transfer because the file is too large. It's most likely a server setting somewhere that you don't have access to.
Since "they don't support 3rd party scripts" I'm guessing you're in a shared hosting environment, which is why something could change on your server without you doing anything. Possible solutions:
In my case solved by switching off Adblocker extention in browser
I tried all the commonly suggested php.ini changes as well as wp-config changes with no luck. Finally found someone suggesting to look at the XHR async-upload.php details in my browser and found out that our firewall was flagging the upload as a trojan (MalAgent.H_9218 to be specific) for some reason. So don't forget to check there, it could identify other possible upload issues as well.
Chrome instructions: Hit F12 and select the network tab, then attempt an upload with WordPress, make sure the filter row is on either All or XHR, in the left bottom pane find and select async-upload.php, in the right bottom pane select preview.
One of our clients, had the same issue.
Finally we found out that the wordpress "HTTP Error" when uploading images, was happening due to a change on the server side. The hosting comany, decided to add APC accelerate to the server in order to increase server's stability and speed. APC accelerate should work only with FastCGI and not with su, so they set PHP to run as FastCGI.
When using PHP as FastCGI, if you try to upload a file larger than 128KB, an error "mod_fcgid: HTTP request length 131388 (so far) exceeds MaxRequestLen (131072)" occurs and causes an 550 internal server error. This happens because the value of MaxRequestLen directive is set to 131072 bytes (128KB) by default. One way to correct this (if server uses Plesk), is to edit /etc/httpd/conf.d/fcgid.conf and set MaxRequestLen to a higher value, for example 15MB (MaxRequestLen 15728640). If server uses cPanel, this change can be done via the WHM of the server.
So, if you can upload images up to 128KB, this is the solution to your problem.
Our problem was that our load balancer ran out of hard disk space. Be sure to setup a log rotation that deletes the oldest logs after a period.
I had the same issue whenever I tried to upload media, except I got the "HTTP Error" on files larger than 124Kb! WP 3.3.1, PHP 5.2.
I called my host and they upped memory to 64M (also changed this in wp-config) and upload_limit to 8 MB (default was 2 MB). This didn't work so I resorted to almost everything else, from tampering with the .htaccess to reinstalling WP to installing a fresh WP on another server, but everything pointed to a server issue. I called the host again and spoke to another technician who increased the allowed HTTP Request Length setting.