I had Agricraft installed at one time til I kept getting server crashes and locking up when people explored in main world as well as making new MystCraft ages. "Skipping Piece with id AgriCraft:Greenhouse" constantly spammed a couple of hundred times then crashed. I removed Agricraft due to that, now every time I make a new Mystcraft world it spams that when AgriCraft is no longer installed on my server or clients. It then holds the Mystcraft world loaded (as if a chunk loader were there) due to it spamming the Greenhouse error. Where is it getting that information from so I can rid it of the lag and spam?

With it removed from my server and clients, how can I get rid of the Greenhouse messages which still continue to spam?

Delete the Mystcraft dimensions that where generated with this error

Does it in my main world too, cannot delete that one. Is there something as simple as a dat file i can edit to remove it?

No clue, maybe use McEdit to regenerate the Chunks containing villages?

Thanks will definitely check that out. When removing any mod and restarting the server, forge will remove all invalid block/item ids via /fml confirm. So the Greenhouse shouldn't even exist. It should be blank of where it was. So I have no clue why it is still saying that. Does/did your mod write to the World\Data folder and append or create any files?

It doesn't, all it does is add a new structure to the Map of structures. I have no idea what is done internally with it. I can look at the code and try to figure out what is going on with the entries of the map.
My guess is they are saved to a file and loaded from there again, this is the only explanation I can come up with as to why it stills try to find the Greenhouse Structure even though the mod is gone. But this is just speculation.

That spam was because of the lack of an empty constructor in the greenhouse code. It's been fixed afaik.