in Add Script Map dialog enter:
Request path: *.wgx
Executable: C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll
Name: VisualWebGUI-Page
Then click Request Restrictions…
Clear Checkbox: Invoke handler only if request is mapped to:
Click OK
Click OK again on Add Script Map
Step2:-

Change the application pool to classic.net apppool at basicsettings tab in under Actions menu.

Step3:-

give iis_iusers read permissions for web.config