This is WordPress error that can happened for many reasons (some server side error happened):
1) Your memory server limits does not allow WordPress to unzip theme or upload ZIP file
2) Unzip extension for PHP is not installed on your server
3) Your themes directory on server does not have write permissions and WP can't upload theme to folder
If you are installing your theme from the WordPress theme installer, but get a message that says “Are you sure you want to do this?”, most likely your web server is configured with PHP settings that are too low to allow the theme ZIP file to upload. Specifically, PHP is configured to a maximum file upload size limit at 8 megabytes or less. The theme ZIP is more than 8 megabytes in size. Thus, the web server is rejecting the upload. WordPress is giving you a rather ambiguous message in response. This is not a theme fault or bug.
There two ways to solve this problem.
- You can ask your web host to increase your PHP limits.
- You can upload your theme via an FTP client.
You should contact your web host and ask them to increase those limits as required:
- upload_max_filesize 64M
- post_max_size 64M
- max_execution_time 120
- memory_limit 256M
You can verify your PHP configuration limits by installing a simple plugin found here. And you can also check your PHP error logs to see the exact error being returned.
Check this official wordpress article how to increase memory limits for your WP:
Check Themeforest FAQ about theme installation issues: