Tara on "Can’t select database"

Hi,
I can not understand this problem: my site is online, but if I want to access the beckend, see “Can’t select database
We were able to connect to the database server (which means your useame and password is okay) but not able to select the ck1j9y4o_wp747 database.”....
I have already seen several times the config.php file and that's fine.
there is something wrong permissions?
What do you suggest? Can you help me please?
thank you
Margherita

We were able to connect to the database server (which means your useame and password is okay) but not able to select the ck1j9y4o_wp747 database.”

This error message generally means The DB_NAME is wrong.