When trying to lock signals or instances that are not in the design, NGDBuild (Translate) reports the following errors:
"ERROR:Parsers:11 - Encountered unrecognized constraint while parsing."
"ERROR:NGDBuild:19 - Errors found while parsing constraint file '<design>.ucf."
This error will occur if a constraint is applied to a net or instance that does not exist in the design. There are two ways to avoid this error:
1. Remove the offending constraint from the UCF file.
2. Select the "-aul" (Allow Unmatched LOC Constraints) switch in Translate (NGDBuild). Any unmatched LOC constraints will be ignored during implementation.