The problem here is if you export full=y or specific users, it will also export the definitions of objects ( I mean definition tablespaces, the tables belongs to) and when you import, it will try to create that tablespace as part of the object definitions and imports into that tablespace if it cant find one thats already defined/precreated.

so your import fails unless otherwise it finds precreated tablespace (specifying ignore=y) or its allowed to create tablespace (ignore=n).

Its just like reorganizing your databases. The best bet is to use Enterprize Manager Reorg utility if you do have...