The root cause of this error was because of the lack of permission to a role. A specific role doesn’t had the permission for location. When the sales orders are created two custom fields will be set with available quantities of that particular item selected in the sales order from two particular locations. Since, the role creating the sales order doesn’t had the permission for locations, the value returned was ‘Field is Restricted’. This returned value cannot be set to the custom field which is a decimal type. So, this error occured.