Immobilizer

[csta]

Hi new to this forum and looking for help already, 2012 Ibiza 1.2 cr tdi it starts then cuts out. Immobilizer warning on dash fault in engine ECU saying disabled and in immobilizer saying enginevecu not authorised. All fuses ok battery good if I reset the faults they return straight away, any help diagnosing this would be most welcome, is the immobilizer part of instrument cluster.