IIS could not remove a program pool because it contains 1 applications

IIS could not remove the program pool because it contains 1 applications, the problem is shown in the following figure:

the cause of this issue occurs:

Virtual directory A is published under the site, and virtual directory B is published under virtual directory A, choosing to use the same application pool.

This problem occurs when you delete the virtual directory a directly, and then remove the application pool that is used by a. Solution:

This lists the applications that use the application pool:

After the change, remove the application pool and it's OK.