Hi Jens,
i have a little Problem with an old self-made ZClass-Product named "CMSFolder". Allready existing objects of CMSFolder are broken since the last restart of the instance. It is really strange because there is no broken-sign in /Control_Panel/Products.
It is still possible to create new objects with CMSFolder, but if i restart the instance, the new objects are broken too. CMSFolder is folderish and it's subobjects of other meta_types are still accessable! Now that you said folderish and ZClass, I recalled a bug when migrating from zope 2.5.1 to 2.6.0, but I can't assure if it is the same bug since you didn't mentioned your zope version and if you were either or not migrating from a previous version. The message is also different, but it could be related. Anyway, just in case you migrated from zope 2.5.x to 2.6.0, you could try:
http://www.zope.org/Members/jmeile/upgradingZope I don't know if this also affects versions > 2.6.0 because by that time there was only 2.6.0/2.6.1 available. This small article assumes that you still have your Data.fs from the old zope instance. If not, the only thing I could think about would be to downgrade, check that everything works, and then upgrade following the instructions -> I'm not sure if this may work; I've never done such thing, for I always keep a backup of my old Data.fs By the way, before doing anything, make a backup of your Data.fs file and then try the instructions. It could be also that you forgot to install a product you used in your old zope into the new one, assumming again you were migrating. So, check the products folder. By the way, posting your zope version, whether you migrated or not, and the previous version you had before migrating would be useful in order to get more help from the list. Regards, Josef