#3 Can't install via update site on Eclipse 3.5

[SeB]

I have a error message during installation :
An error occurred while collecting items to be installed

session context was:(profile=epp.package.rcp, phase=org.eclipse.equinox.internal.provisional.p2.engine.phases.Collect, operand=, action=).
Artifact not found: osgi.bundle,ch.sahits.help,1.0.0.201001051055.
http://sahits.ch/project/eclipse/update/plugins/ch.sahits.help_1.0.0.201001051055.jar

here is a screen copy.
http://my.jetscreenshot.com/3027/20100507-oofd-39kb
SeB.