How to see the code behind a .dll file

Question

Hi,

I am working on an existing application and one of the problems I am facing is this:

One of the .dll files that the existing .net web application is using seems to work differently if I use the code and build the application so as the same .dll file is made. Now, when this .dll file is used by the web application it behaves differently.

Now since this is the only code I have with me I really need to see the code that was actually used to make the .dll file that was originally there.

So, I just wanted to know is there some way to figure out what code was used to build an existing .dll file . Here I am going backwards , from the .dll to the code.

Aatif...