run --mlma with dosage input

Dear GCTA team,

I am trying to do association analysis (--mlma
) with .mldose and .mlinfo input, my command is like  

--mlma

--dosage-mach test.mldose test.mlinfo

--grm test

--pheno height.txt

--out test_on_height

--thread-num 8

Error: the X^t * V^-1 * X matrix is not invertible. Please check the covariate(s) and/or the environmental factor(s).

Whereas, I used plink binary format (.bim .fam .bed) input with the same pheno file, it worked very well. Besides, the grm was generated using .mldose and .mlinfo, so the format should be correct. Do you have any idea about the error? or just because the --mlma does not support the .mldose and .mlinfo input?

Best wishes
Yingjie