General Description: Without pin locking, my implementation containing DCMs completes successfully. However, when I attempt to lock the pins to the same locations using the "Back-annotate Pin Locations" utility, the clock placer incorrectly places the DCMs, and the following error is reported in PAR:
"ERROR:Place:44 - The global clocks ireq2_ibufg/BUFG (BUFGMUX1P) and egr1_ibufg/BUFG (BUFGMUX1S) are locked into a primary / secondary site pair. It is impossible to route all of the clock loads for both of these clocks using the global clock routing resource. Only one of primary/secondary pair clocks have access to any one quadrant via global (high drive/low delay/low skew) routing resources. If these two clocks drive clock inputs in the same quadrant the nets will not be routable using the global clock routing resources."
This issue was fixed in the 6.1i software.
You can also work around this issue by locking the DCMs to the appropriate location.
Example: COMP "u_dcm1" LOCATE = SITE "DCM_X0Y0" LEVEL 1;