Solaris 10 could not NFS-mount from new installed Linux NFS server

A new installed NFS-Server based on Linux shared over NFS some directories.
On the Solaris 10 boxes the directories should be mounted via automount, but
the failed.

Also a manual mount fails:
mount -F nfs linux:/dir /dir


The reason here is, that both, the new linux server and the solaris 10 box, use
NFS Version 4, but Linux and Solaris are not compatible.

What I did to solve this, was setting vers=3 option in the auto.direct-Maps on the NIS server and Solaris was able to mount again.