Everything indicates that the error "HTTP Error" is caused by a change in the Apache FastCGI module (mod_fcgid 2.3.6) that limits the value of the parameter MaxRequestLen to 128KB (very low). Previously this limit was 1GB.
Therefore this problem is likely to occur only on servers running PHP in FastCGI mode and only when trying to upload a file larger than 128KB.
The final and stable solution to this problem is well explained in the link that leaves our friend ntarantino :)
and it works perfectly! :)
but that solution requires access and modify the configuration file of FastCGI. It can be done via SSH or asking the support team of your server to do so.
An intermediate and fast solution I've found, for those who need to solve this problem right now and can not modify that file themselves, is as follows:
- Install the plugin WPlupload (nice and efficient plugin that replaces the WP file upload form)
- In the plugin settings indicate 128kb or less in the "Chunk size"
- Enjoy :)