9.1i Constraints Editor Virtex-4/-5 - "ERROR:ConstraintsEditorC - Please enter a number..."

Description

When I select an empty PERIOD cell, after launching Create Timing Constraints process, the following message occurs: 

"ERROR:ConstraintsEditorC - Please enter a number between 1e-006 ns and 999999 ns"

Solution

To work around this issue, manually create or modify the constraints with a text editor. 

This issue is scheduled to be fixed in the next major release of the design tools.