Problems Convert png to ppm

[kirkalot]

When i use 'nconvert.exe -out ppm -o temp.ppm temp.png' there comes the error:

Error: This picture cannot be written using this format (temp.ppm)

The png file info from nconvert:
nconvert.exe -o temp.ppm -out ppm -info temp.png

temp.png : Success
Format : Portable Network Graphics
Name : png
Compression : ZIP
Width : 283
Height : 14
Components per pixel : 1
Bits per component : 1
Depth : 1
# colors : 2
Color model : RGB
Bytes Per Plane : 36
Orientation : Top Left
Xdpi : Not set
Ydpi : Not set
Page(s) : 1

Any suggestions what can solve my problem?

[xnview]

PPM doesn't support colors, so you need to convert it in 24bits with -truecolors