We are not able to process the Dialog boxes in HTML applications (MDT type URLW) Correctly. Sometimes system is requesting a new logon with user and password while the application data behind the dialog box cannot be accessed.
For example: functions for printing documents or displaying and adding attachments in an application.
You are having this issue because you included an HTML application of the type URLW (Web address - URL - without navigation) in Customizing of MDT. And the application include the function that require the processing of dialog boxes. That's why it is not processed correctly and, therefore, the functions are not available.
Please implement the following correction and import the relevant Support Package.
Support Packages & Patches