Diagnosis
You are editing a step loop and have selected Select loop end,but the screen section below the loop block up to the line where thecursor is situated contains either part or all of another screenelement.

System Response
The system rejects the screen section of this size as a step loop areabecause it is not free.

Procedure
Place the cursor on a line so that the section can form a line free offields that do not belong to the loop block, and repeat the function.
You may have to leave the step loop processing with F3=Back and createthe required space by selecting and moving.