If any I/Os with an IOStandard other than LVCMOS25 (i.e., LVCMOS33) are locked to the bank where the System Monitor auxiliary analog I/Os are used, the PlanAhead software generates the following DRC error:
This is an erroneous warning as the auxiliary analog inputs do not have an IOSTANDARD. The warning can be safely ignored.
Please note that this warning can only be ignored if in relation to the System Monitor auxiliary analog inputs. If both signals in the warning are digital inputs, the warning cannot be ignored.
For details on how to correctly setup the auxiliary inputs, see (Xilinx Answer 29240).