Problem Description

You've upgraded your website's CMS (like WordPress) by uploading the new system files (wp-*) using FTP, but now the site doesn't load. Typically there is a white screen with a parse error showing. If it's just a white screen you can see the error using the log viewer within your control panel to know exactly what the error is.

It's worth noting that this issue could happen with any web application and the solution is likely to be the same.

Problem Resolution

To resolve this problem, re-upload the core/system files with your FTP application set to use "Binary Mode" rather than ASCII mode. This will ensure that any issues with operating system line endings (and other character encoding problems) will not be an issue.

With WordPress this means any files and folders that begin with "wp-" except wp-content and wp-config.php. You'll find similar exclusions for other web applications.