Could anyone please help me with this. On the production site app_offline.htm works only till you start uploading dlls. As soon as you start uploading dlls it throws following error"Could not load file or assembly 'SubSonic' or one of its dependencies. The process cannot access the file because it is being used by another process. Now this clearly shows that IIS is still trying to serve the aspx page?? Is there anything I am missing here?? Any help would be appreciated. I have spent hours googling but to no avail. Thanks in advance. Manisha
I have heard of people having problems with app_offline.htm if it did not have enough content in the file.
Fill it with a couple hundred kb's of Lorem Ipsum text and see if that helps.
Ok this might not be your problem, but if it's the first time it happened you might want to restart your machine. Sometimes a process dies with a lock on a .dll, thus you can no longer use it until unlocked (thus need a restart of the OS).
The other possible problem is that the .dll, or its dependent .dll's, aren't in your path or the correct folder.
Give both of these a look first.
来源：https://stackoverflow.com/questions/373540/why-is-app-offline-failing-to-work-as-soon-as-you-it-starts-loading-dlls