Deployed ASP.NET application reverts to old code base?

We have an ASP.NET application running on a webfarm. When we release a new version and copy it to the production servers, occasionally it happens that after a few hours the application reverts to a an earlier code b开发者_开发技巧ase.

Have anyone else experienced something like this? Would sharing an application pool between two applications running different versions of the code make this happen?

Additional information: 3 x web servers running w2k3/iis6 ASP.NET 3.5

I've had this happen rarely on non-precompiled sites and the solution was to stop IIS and clear out the temporary cache at:

%WINDIR%\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files

Is not a long-term solution, but will address the immediate problem. If not already, it is worth considering deploying the site pre-compiled.