FIFO LogiCore with ISE 8.2 ??

Hi all,

I've created 2 different FIFO with Xilinx Core Generator.

I insert the first one in my design, everything is ok. But when I try to insert the second one, ISE told me that; "Only one design unit of this type is allowed for the same top module"

How can I put my to FIFO in my design?

Thanks Matthieu