If a merchant is unable to modify sizebricks it's possible they lack access to a particular function to modify inventory related to royalty.
The function Name is Inv_Royalty. The roleid needs to have right 6 access, which is view. The script below adds the role if it does not exist and adds role access.
Example for role id 2/3
insert into function values (154,'Inv_Royalty','CAS',NOW());
insert into accessrights values ('2','154','6',NOW());
insert into accessrights values ('3','154','6',NOW());