Error while running MEGAX

I am running the latest version of MEGA i.e MEGAX. I am trying to run the command megacc but it is throwing an error.

My sequences.fas file contains the trimmed multiple sequence alignment (MSA) of 16S rRNA sequences of 1403 organisms in a fasta format. This file was generated after running MUSCLE (produces an MSA) and BMGE ( it performs entropy based trimming on the MSA).

The file “analysisFile.mao” was generated using the GUI based MegaX prototype option. The phylogeny parameters were set to Maximum likelihood, GTR (G+I) etc.

The command that I am running is:

megacc -a analysisFile.mao -d sequences.fas

The error that I get is:

Message = at least 3 sequences are needed for ML analysis

Could anyone help troubleshoot this problem?