Project Navigator ISE

I want an error when I examine my vhdl program with Project NAvigator 
ISE this is the error :
"Bitgen:342 - This design contains pins which have locations (LOC) that 
are not user-assigned or I/O Standards (IOSTANDARD) that are not 
user-assigned.  This may cause I/O contention or incompatibility with 
the board power or connectivity affecting performance, signal integrity 
or in extreme cases cause damage to the device or the components to 
which it is connected.  To prevent this error, it is highly suggested to 
specify all pin locations and I/O standards to avoid potential 
contention or conflicts and allow proper bitstream creation.  To demote 
this error to a warning and allow bitstream creation with unspecified 
I/O location or standards, you may apply the following bitgen switch: -g 
UnconstrainedPins:Allow"

please help me
thanks