There are a number of reasons why an auto update could fail with PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature error message. The most common ones, you need to pay attention to, are:
- You are trying to upload other than .zip file type. Other format is not supported while uploading the theme or plugin in WordPress
- The .zip file is broken or incomplete
- There is not enough disc space on your host for WordPress to be able to unzip and upload the contents of the file
- An error might be thrown by a 3rd plugin or script on your site
If none of above is the reason, you should contact with your host as the problem is definitely on server side.