if you're using OPENQUERY you are executing the SQL "inside" of the AS/400. AS400.S1019865.NSCDEVDATA.WSZZP100 doesn't exist in the AS/400 world. Try this :

Select * from OPENQUERY(AS400, 'UPDATE  NSCDEVDATA/WSZZP100 SET ZZSSRV = ''2006-02-08 09:00:19'' ')

ooops... I just realized this message was posted 1+ year ago

oh well, maybe somebody else can still use it now