Rebuild and Thumbnailcreation fails

Hello,

now I searches the Forum for some time but did not find anything.
I am using Gallery 3 on a german hosting platform (1&1)
I created an album where I uploades 160 pics and it worked very well
then I created a 2nd album where I wanted other users to upload pics and for some pics the thumbs and the resizre pic is not created.
I then tried to rebuild all images by changing the size of the thumb an the resize Image to 201 and 641 px.
but the thumbs are not created anymore at all.

The log of the rebuild dialog says rebuild is successful:
e.g. "Successfully rebuilt images for 'DSC02108'"

but the logfile in the "logs" folder says not suscessful:
2014-01-27 21:23:52 +00:00 --- error: Failed to rebuild resize image: DSC02108

and this is coming for all images which should be thumbnailed and resized.
The folder thumbs and resize is filled with the standard image

the original images shows up in the Album by clicking on the standard thumb image.

the strange thing is that it used to work for some images but not for all.

I am using the "ImageMagick" Tool

the log files of the last few days are attached.

I hope you can help me on this.

Thanks in advance
Gusch