Basically this problem comes up when we work
with Asp.Net Application With IIS Server. I got this error while working with
Asp.Net MVC Application. When I run My MVC application suddenly I got this
error:
“System.Data.SqlClient.SqlException was unhandled by user code: Login failed
for user 'IIS APPPOOL\DefaultAppPool’” and database connection couldn't open.
There are some step for solving this problem.
1. Go to your Run Window and there you type
“Inetmgr” and click oK ( Means Go to IIS Server).
2. Here you will IIS Server window , from this
window you go to “Application pools” and then select “DefaultAppPool” Right
click on it and select “Advance Settings” and click on that.
3. When you will click on Advance settings link
it will open Advance setting window there you select “Identity” (In Process
Modal) and Change the path from ApplicationPoolIdentity to LocalSystem.
When you click on this Path, three dotted
buttons, a window will open from there “Built-in-Account “radio button contain
a dropdown box , from this dropdown box you change this path and the click OK.
