Thank Jim and nitenurse,
for trying to help me. I work under Win7 and so I think a lot of problems have to do with this program! So I tried to replace the wiaaut.dll in ...system32, but I have no chance to do so. Yes I have the rights of an administrator, but not for this action. So I don't wish to do the sophisticated things in that link you gave me Jim.
Nevertheless I am very grateful for helping me!
PS: I have now the solution! In the section "services.msc" there it is to set automatically not only "WIA-Bilderfassung" but also "ShellHardwareerkennung". (By the way I have to apologize my terrible English, I learned this language only in the groundschool - 55 years ago).
greetings
Christian