Windows Sound on Press Enter in TuilLoginDlg

i copied the uLoginDlg form into my Projekt so that i could add a Dropdown list to the Dialog
(We need to decide whether the the Program is used on a Laptop or on a PC with Server Connectivity)
Everything works so far, but when i insert the Password and hit Enter i get a System Sound.
Is it possible to disable this sound?
I read in some Forums that the Sound is produced because the Enter-Key-Press isn't handled propably.
Maybe you got a Tip where to change this behaviour.

Thanks in advance