This error occurs due to settings within The Raiser's Edge. The option can be changed to allow multiple memberships, or the transaction can be processed so that the new membership is linked to the existing membership.

To link to the existing membership:
  1. Open the membership transaction window in the NetCommunity plugin
  2. Click in the RE Membership column cell for the transaction that needs to be processed
  3. Click the F7 key
  4. Mark the checkbox to add the new membership to the existing membership
  5. Click OK
  6. Click Process
To change the setting within the Raiser's Edge to allow multiple memberships:
  1. Click Config in the Raiser's Edge
  2. Click Business Rules
  3. Click Activity Options under Membership Options
  4. Unmark the checkbox for Do not allow multiple concurrent memberships
  5. Mark the checkbox for Warn before adding a new membership if a membership already exists
  6. Go back to the NetCommunity plugin and process the membership transaction