ERROR:ConstraintSystem:2 - The value (TS_macfpga_top/io_mod/clk_dcm) given for the 'tsid' attribute is not valid in its current context. It must satisfy one of the following rules:
The value must be text that matches the regular expression: *i:ts[a-z_0-9\\]+
The value must be text that matches the regular expression:
The Period constraint for this Clock net is actually:
NET "macfpga_top/io_mod/clk_dcm" PERIOD = 9.4ns;
This issue is fixed in ISE 10.1.