A client is reporting an issue wherein the website displays correctly in any browser for most people, but for random certain people an error message is displayed "This webpage is not available". The same people are able to view other sites on those browsers at the same time so it's not a connection issue. The site was working fine for everyone until two weeks ago.
At first I thought it was isolated to IE9, but the client mentioned today it now happened in Chrome as well. in Chrome it also mentions a 101 error.
I did not build the site, and this is my first time working on the site, so I'm not super familiar with it - it looks like a custom theme. Appears that no plugins or major updates have occurred recently.
I did correct some validation problems in the header, but that didn't help. There are other validation problems I've not fixed.
Any ideas? Could it be a server problem? I've googled around and am not coming up with anything.