Plugin not working after update

Hello,

I created a forum in RoR using the acts_as_threaded plugin for the
Esperanto social networking site www.amikumu.com. After the recent
update to the latest version of RoR, adding new posts to the forum is
no longer possible. It seems that the acts_as_threaded plugin is no
longer called, so that fields like "depth" or "left" for forum posts
remain empty and cause the error. I did not make any changes to the
plugin or RoR except that update.

How can I get RoR to make use of that plugin again? Simply re-
installing the plugin won't work as it is no longer in the plugin
repository and I can only find the files as an archive - but I didn't
make any changes to the files.

Thanks for your help!

Judith