I don't, it's bug of forum. I have got error during creation of this topic and get errors during replies to it:
Fatal error: Call to a member function on a non-object in /mnt/home2/ez.no/www/kernel/classes/notification/eznotificationevent.php on line 158 Fatal error: eZ publish did not finish its request
The execution of eZ publish was abruptly ended, the debug output is present below.
Then I press BACK and see form with list of topics's versions (ez publish versions)...
Hmm... Now my class have 102 fields and I plan about 1200 of objects...
The problem you described seems to have been resolved (it was a problem with APC).
Do you plan to use your objects in a dynamic way? By that I mean that they will be used on pages that can not be cached... (pages with personalized content per user)
Uff... I eventually localized error: package creation and following import doesn't work if in class exists URL attribute.
I have tested my class several times for this supposition (remove attribute, export/import package, add it again, export/import package, then change type of it). Export/import stably doesn't work with URL datatype. Maybe URL datatype is not correctly serialized in XML.
Addition: EMPTY URL doesn't work correctly. Normal filled URL normally exported & imported from package. I tested it on standard class Link too.