Undefined variables & Cannot Modify Header Messages

Hi -

I have a website that was working previously and then all of a sudden, I got these messages on the front page of the website and can o longer log in to Wordpress at all.

Error 1 and 2 are attached in the file. They repeat themselves at the top of the front page. Nothing is working now. I don't know how to fix this or where to start. One looks like it is paypal advanced. Do I need to reload the plug in? The other one - no clue.

Thanks in advance!!!