ERROR:Pack:2784 - Directed packing was unable to obey the user design constraint
(LUTNM=Transceiver/INST_PROCESSING_CHAIN.TRX_Data_Chain/INST_FFT_IFFT.FFT_IFF
T_1/V6_FFT_Core_Gen.FFT_Core/blk00000003/U0/non_floating_point.arch_d.xfft_in
st/pe_gen[3].natural_order_input.PE/delay_addr_bf2/SRL16_2) which requires
combining the symbols listed below into a single SLICEM component.
...
The directed pack was not possible because:
The top reasons for failure were:
-> A legal placement was never found for shift register symbol
...