Comment on Stallion Theme WordPress SEO Plugin Support by WordPress SEO Theme Author.
The Stallion Theme zip file is quite big, almost 9MB and can take a while to install. If your host has some settings set low (max_execution_time, max_input_time and possibly memory_limit) it could timeout and I understand the “Are you sure you want to do this? Please try again” is the WordPress error message you get. If it took a while for the error message to show that would strongly suggest a timeout issue.
Come to think of it you can test this by downloading the Stallion Example Child Theme zip file (links on Stallion WordPress Child Themes) and install it like you tried with Stallion.
The Example Child theme zip file is less than 1.2MB so will install much faster so shouldn’t timeout if this is the problem. The Example Child Theme won’t activate (it will install, won’t activate) without Stallion being installed, so won’t cause any harm or anything, if it does install will inform you the Parent Theme (Stallion) isn’t installed if you try to activate. As a side note it’s a good idea to install the Example Child Theme after installing Stallion, makes future main Stallion updates easier.
There’s other things that can cause this WordPress error, but it’s quite a generic WordPress error message so difficult to troubleshoot.
Quickest solution is use FTP to install Stallion. See WordPress Theme FTP Installation Instructions, it’s for another theme (Talian), just replace Talian name for Stallion.
You can also check your upload file size is set high enough. Edit any post, click the add image button and on the window that opens you’ll see a message (close the window after you read the message):
Maximum upload file size: 16MB. After a file has been uploaded, you can add titles and descriptions.
If the MB size isn’t 10MB or more you won’t be able to use the theme installer unless you contact your host to have the Maximum upload file size increased (suggest 16MB) or you change it yourself via a hosting control panel or php.ini file.
Again FTP is the quick solution.
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