unable to accept or deny membership request in a group

I viewed the Pending Membership Requests for a group here:

http://www.curriki.org/xwiki/bin/view/Group_TAHSummerInstitute2009/Members?type=1

I attempted to accept the request.

I got the following error message:

This operation failed. Please try again.

Error number 4001 in 4: Error while parsing velocity page Groups.AcceptMembershipRequestService Wrapped Exception: Failed to evaluate content with id Accept Membership Request Service

I reproduced this 2x in this group.

I also got an error this in another group upon trying to deny a Membership Request:

http://www.curriki.org/xwiki/bin/view/Group_CurrikiTeam/Members?type=1

Upon attempting to deny the member, I got:

This operation failed. Please try again.

Error number 4001 in 4: Error while parsing velocity page Groups.RejectMembershipRequestService Wrapped Exception: Failed to evaluate content with id Reject Membership Request Service

I have reproduced this 2x.