ID:176201 Can't place pin <name> with differential I/O standard -- no legal location available on target device

CAUSE: The Fitter tried to place the specified pin with a differential I/O standard in a location on the target device. However, no legal location is available on the target device. As a result, the Fitter could not place the pin. This error may occur for a number of reasons, including conflicting assignments, such as conflicting I/O standard assignments, or the number of pins in the design exceeding the number of differential I/O pins available in the device.

ACTION: Change or delete the pin assignment.