[Constraints 18-5] Cannot loc instance signal is neither single nor differential

If you get the following error:

[Constraints 18-5] Cannot loc instance 'my_signal' at site X#, Site location is not valid 'my_signal' is neither single nor differential.

1. Open XPS, Clean  All Generated Files
2. Do a Design Rule Check
3. Generate Netlist
4. Exit XPS
5. Delete the Top Level in Plan ahead, re create it.

OH. And don't forget to clean and rebuild the BSP, if you are having this problem it is very likely to added some component to the project and it is not appearing in xparameters.h

Good Luck.