Hi Fabio,
im Sorry - i havnt been in the Office for the last days.
I tried your suggest but it did not make any changes to the result at the printer. 
By the way:
The String has to be (&(cn=LDAP)(&(objectCategory=User)(userAccountControl:1.2.840.113556.1.4.803:=2))) because the printer says that the word LDAP is needed in the string.
Thanks a lot for your help and please dont give up 
)