Error 1370 (42000): execute command denied to user 'readonly@192.168.0.248' for routine 'StoreDB.GenerateSaleReport'

[Asad Raza]

I am using MySQL 5.1.47 (64 bit). I have implemented master slave replication and on slave server database I have created read only user with only commands;

GRANT select on StoreDB.view_items to 'readonly'@'192.168.0.248' identified by 'mypassword';
GRANT select on StoreDB.view_sales to 'readonly'@'192.168.0.248' identified by 'mypassword';
GRANT select on StoreDB.view_profit to 'readonly'@'192.168.0.248' identified by 'mypassword';
GRANT execute on procedure StoreDB.GenerateSaleReport to 'readonly'@'192.168.0.248' identified by 'mypassword';
GRANT FILE ON *.* TO 'readonly'@'192.168.0.248' identified by 'mypassword';

Now user can connect and query views and execute procedures but sometime execute procedure command is denied with "Error 1370 (42000): execute command denied to user 'readonly@192.168.0.248' for routine 'StoreDB.GenerateSaleReport'". To rectify this issue I have to manually execute above command.

Can Anybody help me in this regard? Is it due to replication.

Thanking you in advance.