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Open the NC program in the Editor menu and navigate to block %2 specified in the alarm message. Identify all instructions targeting the following axis/spindle %4 (e.g., COUPLE axis, positioning commands).

Remove duplicate instructions for the same following axis in that block. Consolidate multiple commands into a single instruction; for example, combine two separate COUPLE commands with different parameters into one correctly-formed command.

Ensure you do not accidentally remove instructions for different following axes—only remove duplicates for the SAME axis/spindle %4.

Verify the generic coupling configuration by navigating to Offset → Machine Data and reviewing MD10200 (coupling type), MD10210 (master axis/spindle), and MD10211–MD10219 (following axis definitions) to confirm the intended master-follower structure.

Reload the program, reset the alarm, and execute the corrected block to verify proper coupling behavior.

Review the instruction %3 in block %2 against SINUMERIK 840D programming guidelines for generic coupling (typically COUPDEF or COUPLE syntax). Ensure the instruction follows the correct format: COUPLE <master> <following> <parameters>.

Check Machine Data via Offset menu: verify MD10200 is set to the correct coupling type (e.g., 1 for position coupling, 2 for velocity coupling), and confirm that MD10210 (master axis/spindle name) and the corresponding MD10211–MD10219 (following axis definitions) are properly configured without gaps or conflicts.

If multiple machine data entries are blank or contradict each other, the NCK may misinterpret single commands as duplicates.

Consult the SINUMERIK 840D programming manual section on 'Generic Coupling' and verify that instruction %3 is the correct command type for your coupling setup. If using legacy syntax (e.g., COUPLE versus COUPDEF), update to the version specified in your system's current software release.

Correct the instruction and machine data, reload the program, reset the alarm, and test.

Navigate to Offset → Machine Data and cross-reference MD10211 through MD10219 to ensure each defined following axis has a unique, non-redundant entry. Confirm that the axis/spindle name %4 in the alarm appears only once in this range.

Check the axis nomenclature in your NC program (e.g., Axis2, SPINDLE, Z_COUPLE) and match it exactly to the machine data definitions. Typos or case-sensitivity mismatches can cause the system to consolidate separate axes into one logical entity.

If multiple physical axes were mistakenly assigned the same identifier, assign each a unique name in MD10211–MD10219 and update all corresponding NC program instructions to use the distinct axis names.

Save machine data changes, reload the program, reset the alarm, and verify that each following axis now receives its own unique instruction without duplication errors.