image error: tile cannot extend outside image

dear developers

when i add an image to the cvs version of silva i get the following 
error:

   Error Type: SystemError
   Error Value: tile cannot extend outside image

the very important additional information is that the image is 710x1 
pixels in size (width x hight). the problem does not appear when the 
image's width is equal or smaller than 120 pixels.

regards,
marc


Traceback (innermost last):
   Module ZPublisher.Publish, line 101, in publish
   Module ZPublisher.mapply, line 88, in mapply
   Module ZPublisher.Publish, line 39, in call_object
   Module Products.FileSystemSite.FSPythonScript, line 104, in __call__
   Module Shared.DC.Scripts.Bindings, line 306, in __call__
   Module Shared.DC.Scripts.Bindings, line 343, in _bindAndExec
   Module Products.FileSystemSite.FSPythonScript, line 160, in _exec
   Module None, line 4, in add_object_submit
    - <FSPythonScript at 
/silva/service_views/Silva/edit/Container/add_object_submit used for 
/silva/service_views/Silva/edit/Container/Publication>
    - Line 4
   Module Products.FileSystemSite.FSPythonScript, line 104, in __call__
   Module Shared.DC.Scripts.Bindings, line 306, in __call__
   Module Shared.DC.Scripts.Bindings, line 343, in _bindAndExec
   Module Products.FileSystemSite.FSPythonScript, line 160, in _exec
   Module None, line 52, in add_submit
    - <FSPythonScript at /silva/service_views/Silva/add/Image/add_submit>
    - Line 52
   Module Products.Silva.Image, line 669, in manage_addImage
   Module Products.Silva.Image, line 194, in set_image
   Module Products.Silva.Image, line 469, in _createDerivedImages
   Module Products.Silva.Image, line 514, in _createThumbnail
   Module PIL.Image, line 1136, in save
   Module PIL.GifImagePlugin, line 285, in _save
   Module PIL.ImageFile, line 384, in _save
SystemError: tile cannot extend outside image