Ok, now it is easier to understand what you mean.
I am very surprised that you can not see ML505 in the list of the boards.
I no longer have access to system-generator so I am not able to do this myself, but I am 100% sure that the problem is in the system installation of your software.
Allmost all the examples and classes in Xilinx system generator are using the ML505 as their main platform.
Did you look at the following page and the files in it?
https://www.xilinx.com/products/boards/ml505/reference_designs.htm
There they have provided almost all the information for the EDK and ISE, but I can not find any support for the DSP package.
I am pretty sure that the board definition from the EDK can be used in your environment.
I have attached the board definition of the ML505, you can see if you have this in your system or not.
Let me know if this helps, or else we can try to find another way to solve the problem.
Best regards,
/Farhad Abdolian