The other day I had added a liftetime option to my amember and soon after my entire amember stopped working along with a different sites wordpress admin not working. Anytime I try going to any URL that has amember in it, it goes to a page not found 404 error. I didn't do ANYTHING that might have caused amember to completely stop working like this. the files are all still on my hosting also, so it didnt get deleted. I have contacted my host as well but they got back to me with answers like clean your cookies and stuff that wasn't related. I really need my site to be running or I will be missing out on sales. I check on other computers and other browsers and I get the same result.
Read this thread, it might hold the answers- http://www.amember.com/forum/threads/wordpress-now-shows-a-page-not-found-error-suddenly.15525/