Hi Simon,
There's only me really that uses/replies to anyone nowadays, really I don't work with PHP much any more and should probably shut the forum down and remove the scripts to be honest. I will try and help though if I can.
The problem you're having is to do with the simpleauth scripts using an old function (session_register()) that is no longer the 'best practice' to use in newer versions of PHP.
There are two options - either change your server's php configuration so that it does not show strict messages or change the code so that it doesn't use session_register(). The latter option is probably for the best, although if you constantly get deprecated messages then you might want to disable strict messages in your php configuration file.
To fix the code, try removing the session_register() lines from config.php and perhaps replace it with a single session_start() call. It might even work without the session_start() call because you are using the $_SESSION array variable throughout the scripts and I think session_start() is implicitly called when you do that anyway. I might be wrong though, like I say I don't work with PHP any more!
Alternatively to stop strict error messages being displayed you would have to change your PHP configuration (php.ini file) so that it does not display strict error messages. See here:
http://php.net/manual/en/errorfunc.configuration.php#ini.error-reportingif you read that page you will see this:
Note:
In PHP 5 a new error level E_STRICT is available. As E_STRICT is not included within E_ALL you have to explicitly enable this kind of error level. Enabling E_STRICT during development has some benefits. STRICT messages will help you to use the latest and greatest suggested method of coding, for example warn you about using deprecated functions.
The highlighted bit is what's making PHP show you the deprecated message (the script itself will still work if you don't display the strict warning about deprecated functions, but it's probably best to leave it in and fix the code if you can).