YP passwd - SuSE 6.3 and Solaris x86

Hi I have in SuSE 6.3 a fully functional yp system (users can log in 'a la NIS') on both Suse and Redhat (sorry !) but when they try it from Solaris 2.6/7/8 only root can log in (console of course !). As root I can su - into the user and $HOME and the shell is correct, but this is needless to say - not quite what I would like !. Has anyone any idea why it works in LINUX but not (correctly) in Solaris ?? Any help in this matter is greatly appriciated..... Thanks Ade