If you are using CCSv3.1, then you are most likely using BIOS 4.x. That version of BIOS is not compatible with CCSv6 (or v5 or v4). That is why you are having import issues. You need to migrate your project to BIOS 5.x first by converting the BIOS 4.x CDB files to BIOS 5.x tcf file. See:
http://processors.wiki.ti.com/index.php/Migrating_from_BIOS_4.9_to_BIOS_5.x
If you have any question with this migration, I suggest you post them in the TI-RTOS forum where the BIOS experts there can help you best.
Good luck.
ki