Hello Mary , sorry for the delay ...
Usually when that message pop up , is because the chest has not a own key , and if you have in your inventory some Universal key , you can use it , but there is this secure message for be sure you don't mistake ! Usually players use the Universal key on the Imperial Divine chests...
Please check if you have a key for that type of chest ...
Just from that screenshot which you posted we can't see is a Bug ...
I wish you a good day !
hej Mic, no it had a key.
now i get the message constantly. unreservedly i simply acknowledge the nonsensical message + it runs. the chest opens without leading me to buying the keys.