Status 06 is a catch-all for a command header the card cannot interpret. Three specific causes dominate production: KIc and KID key version numbers differ and are both non-zero; PoR security settings violate the rules (PoR checksum type must match the command, and a ciphered PoR is only allowed if the command was authenticated and ciphered); or the header is structurally malformed — usually a wrong CHL. Because this response is deliberately sent in the clear, it is always readable — use it before guessing at cipher or counter faults.
Usual cause
A catch-all for a header the card cannot make sense of. Three specific causes are worth knowing: the KIc and KID key version numbers differ and are both non-zero; the PoR security settings violate the rules (PoR checksum type must match the command, and a ciphered PoR is only allowed if the command was authenticated and ciphered); or the header is structurally malformed — usually a wrong CHL.
What to do
Because this response is deliberately sent in the clear with no checksum, it is the one code you can always read, which makes it the best diagnostic you have. Check key version equality first, then the two PoR rules, then CHL: it must count from the SPI to the end of the RC/CC/DS, which is 13 octets plus the checksum length.
TS 102 225 §5.1.1 rules 1–2, annex A.2