Any resolve to this... I'm having the same issue.
This grant succeeds...
GRANT alter,control,references,take ownership, view definition ON SYMMETRIC KEY::[BTS_Key1] TO [johnm]
grant alter,control,references,take ownership, view definition on certificate::BTS_CERT1 to johnm;
When johnm does this in the same database, it fails...
OPEN SYMMETRIC KEY [dbo.BTS_Key1]
DECRYPTION BY CERTIFICATE [dbo.BTS_CERT1];
Msg 15151, Level 16, State 1, Line 1
Cannot find the symmetric key 'dbo.BTS_Key1', because it does not exist or you do not have permission.
But, If I grant johnm SA fixed server role... it succeeds.