Problem

When i upgraded Prestashop 1.5 to 1.6.0.11 there were no carriers available even though they were setup correctely in PS 1.5

Cause

This is caused by prestashop changing how they handled the shipping matrix. The matrices that are present after upgrade reflect he carriers that you had there before but the costing data and ranges have not be preserved.

Solution

Go into the shipping methods and repopulated the costing data into the ranges and add ranges as needed as if you were setting these up from fresh