Hi Helipoc,
I wasn't able to find any info on D-HLEY but there is a possible explanation! D-HLEY doesn't exist on any current database at the moment and it could be down to the fact that the reg D-HLEY is temporary until a new owner is found. You mentioned that the EC155 is at Eurocopter Kassel doing maintenance flights, possibly before the new owner takes delivery. C-FORE was c/n 6575 not 6576 which belongs to D-HLTI as seen here
http://www.airliners.net/search/phot...nct_entry=true
Also more info can be found here for future reference
http://www.airport-data.com/manuf/Eurocopter.html and here
http://new.helionline.net/templates/...egister06.html
I hope this is some help to you and I wish you luck in your search!
Let me know if you solve the mystery.
Best regards,
Jim