error while displaying previous page

I have developed a web site npnonline.in
we have typical problem
when clicked on BACK on browser it displays the previous page
however when I use search by typing say "drum" in search area of and click go
results are available
Now I view detail of say CRANTECH (by clicking on the name)
when I click on BACK button of browse i says the page not found
is there a solution for this
why this happens only for search pages (where there is search )

Waiting for your reply and solution if any
thanks

are the search pages created dynamically?

do a search and check if the page showing on the browser exists or not?!

When you submit the form... are you using the POST method or GET?

that doesn't matters
the browser is showing 404, which means it doesn't exists