I upgraded my DNN site last night from 5.0.1 to 5.1.1 using the upgrade package, however, i did need to manually merge my web.config file with the release.config to get it to work.

My issue now is that when i vew pages within DNN i get random versions from previous visits.  For example, I make a change to a module update the page and view again, however, i may get the new page or I may get what i saw five minutes earlier.

I have been through the performance settings in the host menu and set the caching to memory, public and turned compression on.  This has fixed a view state issue i was having.

I have cleared my browser cache which works first up, but after a bit of clicking I get the same behaviour.

any ideas on this issue?

Thanks for the tip Sebastion.

I did that and things looked ok for a bit.  But I am still getting weird behaviour all over the site.  Today I added a page, the page was listed, I went to the page and went to add a module, when I chose the section on the site I wanted to add it to I got a 404 error and then the page had seemingly dissapeard from the tabs list.  I restarted the application and it was magically back again.  I have disabled compression and no joy.

It's like the page is being delivered from cache that is out of date. 

I'm running out of ideas on this one

That was the first thing that i did.  I have never enabled the whitespace filter, however, I have dissabled compression just in case my hoster has it enabled.

I'm still getting this behaviour though.  Usually when adding or deleting modules.  I also from time to time am getting a view state load error where it says that the view state child state needs to match the previous view state.  It seems to be completely random though!

Really frustrating.