Hi everyone. I have 51 Sequences. When I tried to run the MrBayes with this parameter listed below: it cannot execute. These are the parameters

begin MrBayes;
charset first_pos = 1-721/3
charset second_pos = 2-721/3
charset third_pos = 3-721/3
partition_by_codon = 3: first_pos, second_pos,third_pos;
set partition = by_codon;
lset net=6 rates=invgamma;
mcm ngen = 1000 printfreq = 100 samplefreq=10 nchains=4 savebrlens=yes;
sump burnin = 25;
sumt conformat = simple burnin = 25;
end;

Please help and what could be wrong with these parameters.