DFS Locking ASP.Net DLL's through FTP

I am having an ongoing situation where when I try to upload files via FTP that I get an error that the DLL is locked and currently cannot be overwritten. This is only DLLs that this is happeneing to and normal files (aspx, ascx, css etc) can be overwritten fine.

Our Setup

We have 2 webservers that are kept in sync via DFS which is managed from a separate server. They all belong to the same domain. They all do internal transfers on 1GB ethernet cards on a private network.

Our Problem

We develop in VS2010 and build the site we are working on, when it gets to a level where it needs to be checked on the server then its hit and miss whether we can overwrite the DLL's in the BIN folder. I only started experiencing this issue when we migrated from our old, unreliable sync tool to the super Windows 2008 DFS tool. Its a good tool and works well but this is the only thing I can think thats causing this issue.

To actually overwrite the file I need to take down all the sites that are using this base level code which then releases the lock on the DLL and I can upload it.

I come today in desperation, I am fed up and bored of having to take sites down every so often just so I can upload a DLL.

It is my understanding that ASP.Net caches the DLLs into a temporary folder, so god knows why the lock remains on the DLL itself in the BIN folder.

The weird thing is, this does not always happen, it can go for weeks and not do it. Or like recently, its around every day I have to take the IIS sites down so I can upload.

As of writing this, I cannot upload to FTP even though I have taken the sites down.

Could anyone please shed any light on this so I can actually just get on with my work rather than messing with this every ten mins. It's bad enough that VS2010 is so unstable and visual source safe only checks in what it wants without this being an issue as well!

Trying using UnLocker to free the handles.