[l2h] Error while converting imgae

[Christian]

Hi,

I am using Latex2e with png images and all my images are displayed  
right. But during translation I get for every image the following  
message:

Error while converting image
Converting image #10
pstoimg: Error: "/sw/bin/pnmcrop -verbose  < /tmp/l2h53486/p53693.pnm  
| /sw/bin/ppmquant -floyd 256 | /sw/bin/pnmtopng -interlace -trans  
'gray85'  > img10.png" failed: Invalid argument

How could I solve the problem?

Thanks
Christian