The target was already connected on the Linux mount proxy machine. This error can occur if a cleanup was not perfomed, or if the cleanup was only partially successful.
The operation continues.
The Linux mount proxy machine tried to reuse the already connected targets. If the volumes are not correctly mounted, manually disconnect the targets on the Linux mount proxy machine. For example: iscsiadm -m node -T targetname --logout; iscsadm -m node -T targetname -o delete