With a simple DISTINCT I eliminated duplicates. This is what I finally got:
SELECT DISTINCT
Nodes.NodeID AS NodeID,
Nodes.Caption AS NodeName,
Nodes.VendorIcon AS Vendor_Icon,
Nodes.IP_Address AS IP_Address,
Nodes.MachineType AS Machine_Type,
CustomPollerLabels.Label,
Interfaces.Critical_Interface,
CustomPollerStatus.Status
FROM
Nodes, CustomPollerStatus, CustomPollerLabels, CustomPollerAssignment, CustomPollers, Interfaces
WHERE
Nodes.NodeID = CustomPollerAssignment.NodeID
AND CustomPollerAssignment.CustomPollerAssignmentID = CustomPollerLabels.CustomPollerAssignmentID
AND CustomPollerAssignment.CustomPollerAssignmentID = CustomPollerStatus.CustomPollerAssignmentID
AND CustomPollerStatus.RowID = CustomPollerlabels.RowID AND CustomPollerAssignment.CustomPollerID = CustomPollers.CustomPollerID AND Interfaces.InterfaceName = CustomPollerLabels.Label
AND CustomPollers.UniqueName = 'ifInErrors' AND CustomPollerStatus.Status >0 AND Interfaces.Critical_Interface =1
ORDER BY
Nodes.Caption,
Nodes.NodeID,
Nodes.VendorIcon,
Nodes.IP_Address,
Nodes.MachineType,
CustomPollerLabels.Label,
CustomPollerStatus.Status