It does not say which agent u were installing, but presume it to be UD Agent and not BOINC. When u installed it on additional machines, there should have been an 'Existing Member' box. Had u ticked that, would u have been able to add more devices to your first user name. Propose u go back to the later machine, uninstall and reinstall. Hopefully it did not generate too many points, as they forever stay with a user ID.

In the off chance, send an e-mail to contact_us http://www.worldcommunitygrid.org/viewContactUs.do and explain what happened..... maybe they can merge the 2 user ID's.

ciao