Due to a problem with the FFT IP core in Quartus® Prime software version 17.1, you may observe the above error when implementing the FFT IP core in streaming mode, and the input data width is larger than 24 bits. The FFT IP supports up to 24 bits data width only in streaming mode.
For data width higher than 24 bits, use the FFT IP in variable steaming mode which can support up to 32 bits data width.
The FFT IP core GUI will be fixed to allow up to 24 bits data width for streaming mode in a future version of Quartus Prime software.