Spartan 3 Starter Kit Constraints File - constraints

Question

I am not sure if this is the right stack exchange website to post this on, but if it isn't please move it to the appropriate one.
I am facing a small problem in writing my constraints file for the spartan 3 starter kit.
I have read the documentation provided by Xilinx (the manufacturer) and ive been searching online for a few weeks without any luck.
What i am trying to do is link my Netlist interface to any of the 3 40-pin-headers on the board. (See image below)
Usually its very simple, if say i want to interface a button or a led on the board, i just read the connection name on the board, for example one of the buttons is M13 and write in the UCF file something like this :
NET "BTN0" LOC = "M13";
As you can see on the image the headers are named A1, A2 and B1 on the board, but oddly enough, none of the following worked :
NET "TestOutputLine" LOC = "A1(0)"; -- The (0) is to reference a single line on an array
NET "TestOutputBus" LOC = "A1"; -- The bus is of equal dimension of A1 (which is 40)
The errors i got meant that either the target (specified by LOC) does not exist or that the assignment is invalid.
I hope you have some ideas for me.
Thanks in advance
EDIT :
Here is the output from ISE :
ConstraintSystem:59 - Constraint <NET "TestOutputBus" LOC = "A1";>
[circuit.ucf(12)]: NET "TestOutputBus" not found. Please verify that:
1. The specified design element actually exists in the original design.
But i am pretty sure that TestOutputBus exists, as a matter of fact there is nothing else in my design right now, and the correct top level unit is being used.
EDIT2 :
I updated my UCF file, right now it's like this :
NET "TestOutputBus(0)" LOC = "A1(0)";
NET "TestOutputBus(1)" LOC = "A1(1)";
But i get a different error now in mapping :
MapLib:30 - LOC constraint A1:0 on TestOutputBus<0> is invalid: No such
site on the device. To bypass this error set the environment variable
'XIL_MAP_LOCWARN'.
MapLib:30 - LOC constraint A1:1 on TestOutputBus<1> is invalid: No such
site on the device. To bypass this error set the environment variable
'XIL_MAP_LOCWARN'.
Solution :
In order to get the pins 5 and 6 mapped to TestOutputBus(0) and TestOutputBus(1) respectively what i had to use was this :
NET "TestOutputBus(0)" LOC = "N7"; -- A1 pin 5
NET "TestOutputBus(1)" LOC = "L5"; -- A1 pin 6
Note that pins 0 are not mappable thats why i used pins 5 and 6, here are the tables that show the mappable pins for all headers and their LOCs.

Answer 1

As it turns out, there is an address for each usable pin of each header of the FPGA.
The datasheet (http://forums.xilinx.com/xlnx/attachments/xlnx/Spartan/3411/1/S3BOARD_RM.pdf) was helpful especially pages 49 - 51

Answer 2

I copied this from my earlier comment to your question so it would be an actual answer and not just a comment.
You should have LOC constraints in your UCF file for every port on your top-level module. So if you have a 40-bit-wide bus as an input or output at the top level then you should also have 40 separate LOC constraints in your UCF file to make sure that the logical bus in your top-level schematic actually gets mapped to the correct pins on your FPGA. If you are only using two pins, then you can declare the bus to be 2-bits wide and use 2 LOC constraints. The FPGA will treat all unused pins as inputs and ignore them.

Answer 3

I once got the original ConstraintSystem:59 net xyz not found error when i accidentally selected one of my modules as a top module. The pins declared in UCF could not be found in the port declaration of wrong module.
Also i get this error when i have some pin declared in UCF but ommit it in port declaration of top module.