Duplicate does not work with smb

I have a apple server with osx 10.10.5 and a client with osx 10.11.6 and server 5.0.15. file systems

are exportet with smb to the clients.

yosemite clients are working but el capitan clients are not able to copy or create a duplicate file on the

smb share.

there i an error comming up:

"Can't connect to the server because the name or password is incorrect"

any idea what the problem is?

If I using afp to connect it is woking ...

cheers Manuel