Hello,
Yes you are unlucky, It is not my script, but the client.
There happends to be some issues with the itemdefinitions.
The error was also reported recently by someone else in the error/bug section.
http://osbot.org/forum/topic/65181-2322-itemgetname-bug-itemdefinitionforid-bug-still-exist/
The latest Osbot versions have some issues with this.
I suggest you to switch to another method for runecrafting for now.
I'm sure this will be solved soon.
Sorry for your loss, but I can't solve this error within my script.
EDIT:
It happends to work in V 2.3.20.
If you can downgrade to previous versions it should work!
Khaleesi