When I run an incremental design through a newer version of the ISE design tool, the following warning and error occur:
"WARNING:Place:78 - The SLICE component "x" could not be placed."
"ERROR:Place:79 - There were not enough sites to place all the selected components."
When I ran this same design through the previous design tool version, the area group had enough sites for all components.
Changes in the mapper, placer, and router through each release might increase slice utilization in order to improve the performance of your designs. The area group might have to be resized to allow for the increased slice utilization.