On some designs, the customer will not use any of the above libraries. The most common occurence is a user processing an old design from archive which use the CVT libraries (x2-cvt.lib or x3-cvt.lib).
The workaround is to configure an appropriate library from the standard libraries ("appropriate" means that the chosen standard library is from the same family and release as the libraries which are used in the design). Be sure that when the standard library is configured that it appears as the last library. By doing this, the library will be recognized, but no components will be pulled from it. This satifies the SDT2XNF requirement of including a standard library, while not modifying the output. For example:
Another cause of this error is when using OrCAD Capture. If the top- level schematic does not contain any Xilinx library parts (user-created macros or xblox components only), then Capture will not write a Xilinx library reference into the top-level INF file.
Put an unconnected "dummy" component, such as a BUF, onto the top- level schematic. This will cause Capture to write a Xilinx library reference into the INF file. The unconnected gate will be removed by SDT2XNF.