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Review the NC block listed in alarm message (block %2). Identify all axis motion and spindle coupling instructions present (FPOS, COUPLE, LEADLAG, G01, G00, G33, etc.).

Check for hidden commands in subroutines or macro expansions that may be included in the referenced block.

Verify coupling configuration in machine data: check MD20100 (AXIS_TYPE for following axis) and MD20101 (COUPLE_TYPE). Confirm the axis %3 is configured as a following axis type (MD20100 = 2 or 3) with generic coupling (MD20101 = 2).

Separate incompatible instructions into separate blocks. For example: place COUPLE/LEADLAG command in one block, then execute independent master axis motion in subsequent block. Consult ISO 6983 coupling syntax rules in your SINUMERIK documentation.

Verify syntax against Siemens SINUMERIK 840D Programming Guide, Section 'Synchronous Axes' and 'Generic Coupling' to confirm instruction compatibility matrix.

Access Diagnostics > Parameters > Machine Data (MD) via HMI or SINUMERIK Editor. Navigate to axis %3 and verify MD20100 (AXIS_TYPE). Value should be 2 (following axis with encoder) or 3 (following axis without encoder) for generic coupling.

Check MD20101 (COUPLE_TYPE) for axis %3. For generic coupling, this must be set to value 2. If set to 1 (rigid coupling) or 0 (no coupling), instruction syntax rules change; correct coupling type and retest.

If MD parameters were modified, perform NCK reset (soft reset via HMI or hardware reset) to reload machine data into active NCK configuration.

Re-run the NC program. If alarm persists after configuration correction, verify the NC syntax against the active coupling type in the SINUMERIK documentation corresponding to your MD20101 setting.

Check the NC program source for instruction %4 noted in the alarm. Cross-reference against SINUMERIK 840D ISO Programming Manual, Part 1 (General), to verify the syntax is supported on your control (check FB version in Diagnostics > System Information > Software version).

Identify the master axis and following axis relationship. Ensure the master axis motion command (G01, G00, G33) is issued in a separate block before or after following axis COUPLE/FPOS commands, never combined in the same block for generic coupling.

Consult Siemens SINUMERIK 840D Function Manual 'Synchronous Axes and Spindle Coupling' (typically document 6FC5397-*P) for permitted instruction combinations per coupling type. Rewrite the NC block to separate conflicting commands.

After correcting syntax, clear the alarm via HMI Reset button, reload the NC program, and verify the corrected block parses without error.