Random failure with "hdiutil create"

Hi everyone

I'm working on a Shell script supposed to build disk image files with hdiutil. The problem is that it randomly fails. Here is the output :
+hdiutil: create failed - erreur 49168+

That's all I get when using
+hdiutil create -format UDBZ -volname "SFML-1.6-dev-macosx" -srcfolder "/Users/me/sfml/trunk/dist/SFML-1.5-dev-macosx" "$/Users/me/sfml/trunk/dist/SFML-1.6-dev-macosx.dmg" > /dev/null+

When dropping "> /dev/null" and adding -debug, I noticed these lines before the end :
+2009-07-24 18:31:40.620 diskimages-helper\[25526:1603] deleting /Users/lucas/sfml/trunk/dist/SFML-1.6-dev-macosx.dmg+
+2009-07-24 18:31:40.620 diskimages-helper\[25526:1603] DIHelperNBI performOperation: returning 49168+
[...]
+DIHLDiskImageCreate() returned 49168+
+2009-07-24 18:31:40.842 diskimages-helper\[25526:10b] DIHelper dealloc.+
+2009-07-24 18:31:40.843 diskimages-helper\[25526:10b] -DIHelperAgentMaster terminateUIAgentConnection.+
+hdiutil: create failed - erreur 49168+

I don't understand why it would try to delete the dmg file I'm trying to make...
Here is the full log is you want to have look at it : http://pagesperso-orange.fr/c.sobecki/ceylo/data/hdiutil-failure-log.txt

All I was able to find on this error is here : http://lists.apple.com/archives/Carbon-dev/2007/Aug/msg00357.html

Where it says :
+1) Some of the files you're trying to archive are being used exclusively by another process. A couple of people figured that their Anti-Virus software (Norton AV) was to blame.+

+2) Disk space is low, and the hdiutil tool cannot perform its internal caching.+

+3) A file system error which is not detected by Disk Utility prevents proper accessing some crucial files. Repairing the disk using "Disk Warrior" did help.+

+4) Files which were put into the trash can but were not deleted yet cause problems when tried to being put into the disk image.+

1) I'm not using an antivirus
2) I've about 70 GB remaining
3) But why would it be random ? It's always the same files that are being packed.
4) I've no file in my trash.

Does anyone have an idea why it fails ?

Thanks
Ceylo