LOMETS prediction for sequence containing unknown amino acids

Hello,

I have a problem... I have a sequence:

XSAAGPGXMSFTFASPTQVFFNGANVRQVD

it contains two unknown amino acids (X)... it is correct FASTA format...

but unfortunatelly, LOMETS does not work well with this... is there another sign to use for unknown amino acids which can work with LOMETS? or do you have any idea why does it not work?

Thanks for your answer,

Br,

Andrea