This can happen if IIS Handler Mappings have duplicate entries.
To resolve the issue, complete the following:
From the IIS Manager, select the Server level in the tree view.
In the middle pane, open Handler Mappings. Note you have an ArcherAsyncUploadHandler here
3. Try clicking on the Handler Mappings in the Archer site level. You will see the following error:
There was an error while performing this operation.
Filename:\\?\C:\inetpub\wwwroot\RSAArcher\web.config\ Line number: 322 Error: Cannot add duplicate collection entry of type 'add' with unique key attribute 'name' set to 'ArcherAsyncUploadHandler'' Image description
To resolve this issue, remove the ArcherAsyncUploadHandler from the Server level.