I looked through my logs and found this:
Jan 5 21:14:51 DiskStation iscsi.cgi: iscsi_lio_target_portal_group_add.c:38 Failed to do command 'mkdir -p /sys/kernel/config/target/iscsi/iqn.2000-01.com.synology:diskstation.name/tpgt_0 1>/dev/null 2>&1', errno=-1
Jan 5 21:14:51 DiskStation iscsi.cgi: iscsi_lio_target_portal_group_add.c:39 Unable to create iSCSI Target Portal Group ConfigFS directory, iqn.2000-01.com.synology:DiskStation.name 0
Jan 5 21:14:52 DiskStation iscsi.cgi: iscsi_lio_target_iqn_remove.c:30 Unable to locate iSCSI Target IQN: /sys/kernel/config/target/iscsi/iqn.2000-01.com.synology:diskstation.name
Jan 5 21:14:52 DiskStation iscsi.cgi: iscsi_util.cpp:350 iscsi_util.cpp:261 Failed to create target
How do I fix this?