GROUP BY ERROR

[Dvilches_]

Hello there,

Does anyone knows why this poblem happen?: 

This formula is invalid or incomplete: 'Calculation error in measure 'SELLOUT'[RNGSDFGD]: The expression refers to multiple columns. Multiple columns cannot be converted to a scalar value.'.

The code:

= GROUPBY(
SELLOUT;
SELLOUT[STORE ID];
SELLOUT[8D CODE];
"RNG"; SUMX(CURRENTGROUP();SELLOUT[RANGETGT])
)

Thanks!