Ok, got it. Being new to android (only bought my device 1.5 months ago),
I did not realized that the apps has to be completely shutdown (forced closed?).
Apparently it was still running in the background, that is why my file manager
said the function cannot be completed. I shut down the device then use my file
manager to move the downloaded maps to external SD before initiating Locus
again, and that solves it. Thanks again for all the replies. A great apps and a lot
of friendly help from this forum.