Sounds like a bug. What version are you running?
You can report this at 
jira.xwiki.org.
Thanks
Caleb
On 11/08/2010 08:05 AM, Felipe Giotto wrote:
  Hi everybody!
 I just started using XWiki and I'm liking a lot! But, I was having
 some trouble with attachment versioning. I was using XWiki with Tomcat
 as a Service with Windows Server and I couldn't sotre more than one
 revision of my attachments. All the old attachment revisions were lost
 after restarting XWiki...
 The fast workaround is: Configure Tomcat to run as a User account, not
 a System Account (in the service properties window).
 The explanation is: XWiki uses a "kind of" CVS repository to store the
 attachment revisions. When Tomcat is running as a service with a
 System account, XWiki stores the author name with a "$". This
 "corrupts" the repository and XWiki can't load it again! Using a User
 account is a simple workaround for this! Maybe this could be changed
 in the next version....
 Best regards!
 Felipe Luiz Christófolli Giotto
 Linux User #497287
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