Hi ozp,
Currently, there is no way to set a limit on registrations besides date restrictions. However, when registration is full, you can manually close the registration type. I've created a Bugzilla entry (
http://pkp.sfu.ca/bugzilla/show_bug.cgi?id=2909) for this feature so that we can consider it for inclusion in the next release.
Regards,
Alec Smecher
Public Knowledge Project Team
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Don't miss the First International PKP Scholarly Publishing Conference
July 11 - 13, 2007, Vancouver, BC, Canada
http://ocs.sfu.ca/pkp2007/