The following error occurs during the implementation "Translate" step:
"ERROR:NgdBuild:686 - A parsing error has occurred while reading filename.ucf The value '15' at column 38 on line 3 is invalid."
This issue occurs when a LOC constraint is missing the "P" for packages that require it.
From the 4.1i and newer Constraints Guide
INST "instance_name" LOC=pin_name;
INST "instance_name" LOC=FBff;
INST "instance_name" LOC=FBff_mm;
"pin_name" is "Pnn" for numeric pin names or "rc" for row-column pin names
"ff" is a function block number
"mm" is a macrocell number within a function block
From the 3.1i Libraries Guide
LOC Syntax for CPLDs
"pin_name" is "Pnn" for PC, PQ, or VQ packages; "nn" is a pin number
The pin_name is "nn" (row number and column number) for PG packages. See the appropriate data sheet for the pin package names (e.g., p12). Examples are LOC=P24 and LOC=G2; this form is valid only on pad instances.