I'm no expert in this situation when it comes to errors. MirkoSP or McDirty might be better sources here, since I only know how to work the things, but don't know much about the software specifically. XD
You might consider uninstalling/reinstalling Avisynth and then put the new plugins back in? Because it does say this in the installation bit:
If you already have other AviSynth plugins installed, then I highly recommend you remove them and start over from a fresh new installation of AviSynth, because otherwise conflicts may occur between your existing plugins and the plugins contained in this pack. If you don't want to lose your existing plugins, you can move them to a different folder and then copy them back later, as needed. Otherwise, the installation process should be straightforward.
You might also consider just installing the full AMVAPP on the link I provided if you do decide to do a fresh installation.