I'm not 100% sure why your admin page is blank now. Was this happening before you install LAMS?
Now regarding the Warning and Notice statements when you turn debugging on, those are due to a PHP XML dom library that we had to use to get PHP 4 users.
The main problem we had with PHP is that it doesn't come with a DOM parser unless you are using PHP 5 _and_ you compile it with DOM (see PHPinfo()). If you have PHP 4, then you don't have many options but to use external libraries.
Since Moodle requires PHP 4.3 as its minimal requirement, we had to opt for PHP DOM XML library, which support PHP 4.10+.
However, this library is rather old, it seems to use some deprecated methods and these warnings get thrown on the screen.
If you have Moodle debugging turned on, then the LAMS2 module to add lessons will simply not work
Having said that though, if debugging is set to minimal, then you shouldn't have any problems.
I believe I read that Moodle 2 will require PHP5 so hopefully we'll be able to use the default built-in DOM support rather than using external libraries.
Now, if you do use PHP5 and DOM is built into it, I think it would be pretty simple to use that rather than the phpdomxml lib.
Let me know if that's the case with your server, and then give tell you were to change the code and all... (I just need to remember how to do this)
Posted by Ernie Ghiglione