One other thing I noticed is that the encode CCSDS, decode, CCSDS, and BER blocks all operate on packed bytes. (See e.g.
https://wiki.gnuradio.org/index.php?title=Encode_CCSDS_27). To do this you would change your random source to output from 0 to 256 byte values. Also, considering the output of the decoder block are packed bytes you should probably skip the byte->float and binary slicer after your decoder and just input it's output directly into the BER block. Finally, looking at the
https://wiki.gnuradio.org/index.php?title=Decode_CCSDS_27 page it seems the delay out of the decoder is 4 bytes, so you could add a delay of 4 between your source and BER block to align the two streams.
Jared.