App pool crash : IIS Express vs Local/Server IIS

I have improved some external dll in a web API application. If I run it using Visual Studio's IIS Express then it works fine. But if I depoy it to local or server IIS then App is crashing the App pool. Is there any way to find the problem?

Application is crashing, when I call constructor of external dll.

Solution

I changed app pool settings on local/server IIS.

Open IIS - Application Pools - select your application's app pool - advanced settings

Set

Identity : LocalSystem

Rapid-Fail Protection - Enabled : False

I don't know how but it fixed my issue.