When a CLKFX pin of a DCM is the result of dividing the orginal value by 0.66667 (or other repeating value), the timing tools round half of the number down and the other half up. This produces a very small requirement and a very large negative slack value. When is this going to be fixed?
This problem has been fixed in the latest 7.1i Service Pack available at:
The first service pack containing the fix is 7.1i Service Pack 1.