Welcome @Cravo_Adri!
It could be helpful to have a full reprex to better understand the problem -- especially as it relates to the data.
I attempted your code on the mtcars data frame, and it works fine for me. This leads me to guess (although I cannot confirm) that there may be an issue with the column types for your 6th and 7th columns (wt and qsec are each numeric/double columns in mtcars) -- also, are the columns you want to use the 6th and 7th columns in your data?