Hi Lenni,
Great to hear you are interested in pushing out the extension library for people to use. First of all, let me just clear up why you are seeing an issue when opening your Teamroom application that is on your server in a client and its looking for the extension library. It is because although the Teamroom application is on your server when it is opened in XPages in Notes Client (XPiNC), it is getting executed locally in the client. Therefore if your application uses extension library controls, you will need to have the extension library plugins installed in the clients using same application.
I am guessing you installed the extension library in Domino Designer using the Eclipse Update UI Manager which you enabled via the preference page. If you want to install the extension library in the notes client where no designer exists, then enabling this UI can be done by adding this line to a file in your client install.
Edit /framework/rcp/plugin_customization.ini and add the following entry:
com.ibm.notes.branding/enable.update.ui=true
We are currently evaluating alternative install solutions for Upgrade Pack 1 so this is likely to become easier in the future.
thanks,
Padraic