Coiled Tubing Lockup is a condition in which no coiled tubing forces or movement can be transmitted downhole.

Explanation:
One benefit of coiled tubing over slickline or wireline is that it could be easily run in deviated or horizonal wells.
However, in some situations even with coiled tubing we are unable to reach the targeted depth.
From the surface we are running coiled tubing into the wellbore, but at the end it is stationary and is not further moving give rise to the situation known as lockup.

Causes of Lock-up:
Frictional forces
Buckling of colied tubing string