visitors getting ERROR page too often

I hope someone can help. In the past some people I know had mentioned getting an error message when visiting my site. I thought I fixed it with some help, but that person is no longer helping me, and I fear it wasn’t fixed in the first place. Too many people who come to my site only stay a second, even after I see that they were looking for my site–I.E. after articles in the New York Times and the LA Times. It doesn’t make sense, and I don’t know how to fix it or what pecentage is actually getting the message.
My site is http://www.literaryrags.com
Also, people using certain versions of Macs can’t see the BUY button??? But the above problem seems more pressing.
Thank you for any help!!!