merge-methcounts sites not sorted error

Question

[Connor]

I am using merge-methcounts to merge two methcounts files:

 B73_253-1.meth and B73_249-1.meth

I used the following command:

 merge-methcounts B73_253-1.meth B73_249-1.meth -o B73_2n.meth >& log &

As merge-methcounts runs, the B73_2n.meth file is written correctly, but the program terminates before finishing and I receive the following error:

 error: sites not sorted in B73_253-1.meth

How should I resolve this error?