On clicking up the EMAIL button on the Transaction record, i need to set the Template field on the Message record (EMAIL) in accordance with the Subsidiary. It says THAT_RECORD_IS_NOT_EDITABLE. I use beforeLoad userevent script, deployed on Message record. how can i achieve this? Could anyone please help?

Show code. I'm pretty sure I've done something similar. Not sure why you would be getting that error.

thank you, its done in another way