This could be because your hosting server is having a problem, it could be a script problem or it could be an error with the .htaccess.

1. If you have just changed your .htaccess then go review your changes (perhaps restore the backup you made just before you altered it). If this fixes it then seek help with the alterations you wish to make.

2. Run http://yourdomain.com/manager/info.php which is a simple one line php statement that returns the status and capabilities of your PHP. If this page shows an error then you will need to contact your hosting support company.

3. Next try running http://yourdomain.com/backend/sitestatus.php - if you get the same error then your host may have updated their ioncube loaders. To check that run http://yourdomain.com/ioncube/ioncube-loader-helper.php which will report any issues and provide advice to fix it. If this file fails to run then it is most likely the web server is having a problem and you will need to contact the hosting company for support.