External relationship importing

I have 02 separate projects, Client Engineering schedule and construction schedule, I wish to link relationships between 02 projects.

If I do assigning manual relationship by selecting project, “it Works” and it consumes more time. But If I try to import activity relationships between projects , “it fails” and am getting error note as below.

Excel Import log started : 21-Jun-16

INFO: Importing Global Data...

INFO: Importing Project Data...

INFO: Importing:

WARNING: TASKPRED: Failed to resolve foreign key for field Activity ID with value A2EC0850. Field cleared.

INFO: Saving:

ERROR: pred_proj_id is null for TASKPRED: toString invalid state

INFO: Saving Data to Database...

INFO: Deleting Unreferenced Data...

Kindly advise in this regard.

Regards,

Syed