10 years later…
As indicated here: https://forum.audacityteam.org/t/2f-error-message/61863/1
There’s an incompatibility with the original version of the effect and current versions of Audacity.
This version fixes the compatibility problem:
vibrato.ny (1.74 KB)
Note: This does NOT fix the limited length issue.
Ideally the changes in the previous post should be incorporated to fix the length limitation.