No other errors. Here's a full console - started up the game, loaded the save, added a slave to the (previously empty) farm, then tried clicking the panel buttons (the workers button, oddly, worked fine this time. Maybe because I had no farmhands assigned)
Viewing post in Aric's Expansion Rebred
Was this a new or existing save? And any other mods installed? Finally, have you reinstalled the mod and/or double checked the install steps or video? That includes deleting the backups folder, as it looks like your Mansion.gd is acting like the farm’s variables aren’t a thing (ie: vanilla code) in your globals & farm file.
Might have the solution for you in my recent comments. Fixed it for myself and one other person. On old saves you don't have all of the code you need so you need it added. Follow the post where I said "Okay well this was miserable" first and then after that do what is in the "Buckle up buttercups" post.