There are several common reasons why you would get the frustrating error message advising you of an HTTP error. WordPress does provide a few solutions for them, all require a bit of guts working with some code. We’ve presented the most common that a novice user should be able to do on your own.
Sounds obvious, we know, but sometimes we get in a rush and leave an unallowable special character in the name of the file. Shorten the file name, leaving no spaces, and this may do this trick.
Reduce the size of your file. There’s very few reasons we can think of that you would need a very large image over 1MB on a website, the majority of images on webpages should only be about 250KB or less.
If your file is larger then that, reduce the pixels using your favorite image editor like Paint, Photoshop or even Microsoft Windows Picture Manager. Your file width shouldn’t be larger then the container it is displayed in. For example, if you are displaying your image in a container that is 900px wide, you don’t need a 3,500px wide image! Google will ding you for that, by the way.
After reducing the pixels, then compress the image, or as Red Palmers call it…. “tiny-fy”. We prefer to use tinypng.com for all of our image compressions. If you haven’t developed the habit of running 100% of your uploaded images through this service first, now is a good time to develop this much appreciated habit. If you don’t… another Google ding.
Update your WordPress platform, then your theme, then your plugins (in this specific order). We found this to be the case with three of our websites, which prompted this particular blog post. An out-of-whack W3TC version was not compatible with the (no kind adjectives here) 5.0 WordPress roll-out.
The following is where things get a bit more challenging, and you will need to seek the assistance of your web developer or skilled friend.
Via FTP, you will need to edit a couple of files. You may find you have to do this for themes that use builders, as their native strings are very long to store in the sql database. If you feel brave, you should be able to do this. Use a text editor to open these files if you are unfamiliar with working with them.
define( 'WP_MEMORY_LIMIT', '256M' );
php_value memory_limit 256M
memory_limit = 512M