Wrong/impenetrable error messages

Installing the as7 plugin, I get this somewhat weird error message:

Not loading plugin [foo] due to incompatible Forge API version [1]. To remove this plugin, type 'forge remove-plugin foo:1:s1' inside Forge.
Not loading plugin [foo] due to incompatible Forge API version [2]. To remove this plugin, type 'forge remove-plugin foo:2:s2' inside Forge.

Where foo is coming from, I don't know, and what the [1] and [2] are is also not clear

Issue is both the the fact I get the error, and the fact the error message is basically gibberish.