After creating an EDIF-based ISE project, I launch Constraints Editor and create several constraints. Upon saving the constraints, I receive the following message in the console:
"ERROR:ConstraintsEditorC - Unable to create constraints."
To work around this, manually edit the UCF.
This problem has been fixed in the latest 10.1 Service Pack available at:
The first service pack containing the fix is 10.1 Service Pack 1.