Hey Nikolay
Thank you very much for your help. I want to use the default SAP login Page, so I didn't specify a login page.
From Specifying Authentication for Java Applications - Using Central Development Services - SAP Library:
If you do not specify your own login and error pages, the AS Java uses the corresponding pages of its own default logon application. We recommended that you use the default pages to ensure a consistent user experience across all applications and because those pages contain built-in security features.
The BASIC authorization method doesn't operate via form (i.e login page). It opens a "login popup" in your Browser whenever one tries to open a page. Unfortunately HTTP BASIC has some security flaws and should not be used anymore.
I suspect that something on the run time environment is flawed. Any ideas?
Best regards
Fabio