General Description: When guiding the PAR without guiding the MAP and checking the box " match guide design exactly", the following error happens in PAR: FATAL_ERROR:basnd:basndutils.c:130:1.6 - Internal Error - signal has a loop, router problem? Process will terminate. Please call Xilinx support.
This is a bug in M1.4.12. It has been fixed in M1.5. Current workaround is to uncheck the box "match guide design exactly".