When running Place and Route targeting a Spartan-3E Automotive device, I receive the message:
"WARNING:Route:438 - The router has detected an unroutable situation due to local congestion"
You can run the same design with a different value for the starting placer cost table. The starting placer cost table entry for PAR is specified with the -t option. Syntax of the PAR command: par -w -ol high -t 20 mapped.ncd routed.ncd.
This issue will be fixed in the next IP Release.