"Page not Found" or "Server Down" errors when using back end

I launched my site this past May using WordPress 2.9.2 and starting a couple of months ago when I navigate through the back end, sometimes I am directed to my default “page not found” page and sometimes I get a “server down” error. The server hosts other sites, only one of which has also been down.

This has been happening more and more frequently. It occurs when:
* I login
* I publish or edit a post
* I attempt to navigate to the:
– plug-ins page
– widgets page
– media page
– links page

Usually I can hit refresh or shift + refresh and I will be taken to the page I want to be at. It does this randomly. When it first started happening when I tried to show other people, it would never happen but now it happens all the time.

The front end has also been occasionally getting the server down 500 error.

It also has happened a handful of times on another wordpress site I have, version 3.0.1 with a different theme and all different plug-ins. I’m worried that it will happen more frequently.

Any ideas?