Another user deactivated your card
If the primary cardholder made changes to the account without an authorized user's knowledge, the user's card could be declined. The cardholder may have reported his card lost or stolen, in which case the card issuer would typically deactivate all cards under that account while it sends a new one, says Opperman.
Passing along information about changes to your card's status is essential when sharing a credit card with others, especially if you're the primary cardholder making decisions that affect other users. Opperman says that sometimes primary cardholders fail to relay important decisions.
"Sometimes these authorized users will try to use their card, and then they'll find out, 'Oh my gosh, the cardholder removed me, or the card was deactivated and they didn't inform me.'" Like in any relationship, communication is key.