ID:15855 Output port <name> of I/O output buffer "<name>" has too many fan-outs. The I/O output buffer is allowed to drive only one top-level pin, but it has <number> fan-outs.

CAUSE: The specified I/O output buffer primitive has too many fan-outs. The output buffer can drive only one top-level pin and nothing else.

ACTION: Check the design and make sure that the output buffer is connected properly to only one top-level pin.