WEB client upgrade - login page not displayed

After upgrading from 2015.1 version directly to 2015.11.73 no login page was shown. Instead I got an error message such as

Is there any solution?

Im am 100% sure I went through all migration steps correctly.

This error could be very probably easily fixed by changing your web.config file: element <modules> under<system.webServer> must have attribute runAllManagedModulesForAllRequests="true"

for example

   <modules runAllManagedModulesForAllRequests="true">