Since you're using a DCM, you don't need to put a period constraint on
clk4x. You only need to specify the period on the clkin to the DCM and
the tool will automatically propagate this constraints to the DCM
outputs with correct phase adjustments. This of course requires you set
up the DCM attributes correctly.

You can run the timing analyzer to see why you got a very high timing
score and fix code and/or constraints accordingly.

HTH,
Jim
http://home.comcast.net/~jimwu88/tools/