Thumbnails created with a zero (0) file size and thumbnail image does not appear in Share document library

Thumbnails are always created with a zero file size. This occurs, for example, in Share when uploading a jpg, when executing a javascript action to generate a thumbnail or uploading a Share profile avatar.

The following message is generated in the log when DEBUG is set:
15:03:07,197 DEBUG [org.alfresco.util.exec.RuntimeExec] Execution result:
os: Windows XP
command: [C:/devtools/ImageMagick-6.5.7-Q16/imconvert, C:\devtools\apache-tomcat-6.0.18\temp\Alfresco\ImageMagickContentTransformer_source_6794085110837159309.png[0], -thumbnail, 100x100, C:\devtools\apache-tomcat-6.0.18\temp\Alfresco\ImageMagickContentTransformer_target_9019625159893596094.jpg]
succeeded: true
exit code: -1072365564
out:
err:

Solution posted by Nicola Prando in the following post:
http://forums.alfresco.com/en/viewtopic.php?f=36&t=23723&p=83059#p83059

Solution summary: Add the following entry to imagemagick-transform-context.xml:

<entry key="SYSTEMROOT">
<value>C:/WINDOWS</value>
</entry>