Hello,
that seems to look like the issue described here. Argunet should run just fine without the plugins, though they come in handy if you want to export the argument-maps as pdf, jpeg-images and the like.
What regards your decision: We received reports about other issues and since there won’t by any further Argunet-releases, these problems won’t get fixed. So you might consider to use another tool in order to avoid further frustration. The former Argunet-Team switched to the new Argdown. Some background information about the differences can be found here.
Hope that helps.