I believe that you should follow the upgrade process in order to use 4.0 as the contentclasses management (among other things, of course) has changed since 3.8.x so I think the better way is to follow the upgrade process fro 3.8.x -> 3.9.x -> 3.10.x and then finally 4.0
hth!
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Xavier Serna
eZ Publish Certified Developer
Departament de Software
Microblau S.L. - http://www.microblau.net
+34 937 466 205