At first, install the latest Software version (
http://octoplusbox.com/en/download/software/).
If You want to write any IMEI, do the next:
1. Make Factory data reset and wipe cache partition.
2. Install the latest Software version (
Software).
3. Root the phone.
4. Write the special firmware from the Support Area ("sm-g7102_special_modem_to_repair_any_imei_4_3").
5. Ennet IMEI and repair it.
6. Post here full Software log with all of these actions.
Also, You can try to write Cervices IMEIs from the Software list. The procedire is the next:
1. Make Factory data reset and wipe cache partitoin.
2. Write firmware ("SM-G7102_for_Unlock_and_Repair_IMEI_4.4.2.oct") from the Support Area.
3. Select service IMEI from the Software list.
4. Connect powered-on phone to PC via USB cable.
5. Install the necessary driver.
6. Click "IMEI fix" button.
7. Follow software instructions (prompts).
Also, if You have IMEI Certificate for this device, You can write it.
Look here:
http://forum.gsmhosting.com/vbb/f684.../#post10690374,
http://forum.gsmhosting.com/vbb/f684.../#post10690142,
http://forum.gsmhosting.com/vbb/f684.../#post10756089,
http://forum.gsmhosting.com/vbb/f684.../#post10742528,
http://forum.gsmhosting.com/vbb/f684.../#post10724579.