Somewhere in http://publib.boulder.ibm.com/infocenter/iseries/v5r3/index.jsp>here
there are details on how library(members) are handled.
Your problem seeems to be the basic member name is leant to be up eight chars and anything after a '.' is interpreted as a type (somewaht like .html, .jpg .exe etc)
however you can only store one type of data in a library object. So if your first memeber was premier.stuff than all the other member must have ".stuff" as a suffix if supplied.
The official 400-eze for a member is:
member
Different sets of data, each with the same format, within one database file.
You could probably get away with deleting everything after the first period from your member name.
Sorry if this isnt too clear but when the iSeries was designed they ignored every OS designed up till that point and started again from scratch. The results take some getting used too.