Can't convert some PNG to JPEG using NConvert

[wint]

Hello
Had some problem with convert PNG->JPEG via nconvert (with XNConvert all good - i used only Transparent color option and all good)

Via nconvert had error "Error: This picture cannot be written using this format".

Tried insert -merge_alpha, no success..... after tried -truecolors, error disappeared but in exit I had bad quality image with a bad shadows

Would be so grateful for help. thank you.

1aac2af3_397f_11ed_ba57_3cecef5e3ecc.png

1aac24c1_397f_11ed_ba57_3cecef5e3ecc.jpg

[xnview]

it's an 8bits picture, you need to convert it into 32bits before (-32bits)

[wint]

Thank you so much sir!!!!