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Enter EDIT mode and search the active program for all DO statements. Look for DO4, DO5, or higher numbered loops (e.g., DO4, END4).

Verify each DO statement has a corresponding END statement with the same loop number. Valid syntax: DO1...END1, DO2...END2, DO3...END3 only.

Correct any loop numbers exceeding 3 by restructuring the macro logic or consolidating nested loops to stay within the three-level limit.

Reset the alarm using the RESET key and run the program in single block mode to verify proper loop structure execution.

In EDIT mode, list the program and identify all DO-END pairs. Create a table matching each DO number with its corresponding END number to verify pairing.

Check nesting structure: outer loops must use lower numbers (DO1 outermost), and inner loops must be completely closed before outer loops close (DO1...DO2...END2...END1).

Correct any mismatched pairs by changing the END number to match the DO number, ensuring proper sequential closure of nested loops.

Verify using parameter 3202 bit 6 (macro statement format check) is set to 1 to enable strict syntax checking during program execution.

Changing parameter 3202 requires parameter write enable (PWE) and a control restart to take effect.

In EDIT mode, use the search function to count all DO statements and END statements separately. The quantity of each numbered loop must match (e.g., number of DO1 = number of END1).

Review macro subprogram calls (G65, G66, M98) to ensure DO-END loops are not split across main program and subprogram boundaries, as each program must have complete loop structures.

Add the missing DO or END statement with the correct loop number to complete the pairing. Ensure proper indentation for readability and verification.

Check DIAGNOSIS screen 300 (macro alarm history) for additional details on which program line triggered the alarm by pressing SYSTEM > DIAGNOSIS > enter 300.