Error converting image file! [netPBM]

[zipperrr]

Hey, I have searched the forum, but didnt find any information
about this error :"Error converting image file!" it appears when i try
to convert thumbnails or resize images, i have netpbm binaries,
my server is running safemode, but i have done all catalogs chmodded 777 but it doesnt work, i can upload. the only problem is the thumbnail part, Please i really need help with this...
sorry for my bad english i am swedish...

Mvh Jens