Using SREFFECTS element

[Chae]

I used ILMATRIX for the fast tracking and it worked as expected. When I add the element SREFFECTS to the lattice line, it produced the errors below:
tracking step 1
1 matrices recomputed for periodic Twiss parameter computation
statistics: ET: 00:00:00 CP: 0.02 BIO:0 DIO:0 PF:0 MEM:0
matched Twiss parameters for beam generation:
betax = 6.600000e+00 m alphax = 0.000000e+00 etax = 0.000000e+00 m etax' = 0.000000e+00
betay = 2.100000e+00 m alphay = -0.000000e+00 etay = 0.000000e+00 m etay' = 0.000000e+00
generating bunch 1.0
dumping bunch
tracking 100 particles
27 Jul 17 11:03:39: This step establishes energy profile vs s (fiducial beam).
27 Jul 17 11:03:39: Rf phases/references reset.
Problem with SREFFECTS: no twiss parameters were computed
It may be necessary to pre-compute twiss parameters using an additional
twiss_output command with output_at_each_step=0

Any suggestion to avoid this error will be appriciated.

[Chae]

I added twiss_output command as the error message suggested. It works now. Thanks CY.