Web discussions of Tenvis seem to refer to it "copying" the Foscam line, as opposed to being related to it, so the theory could be off-base. However, the level of resemblance seems to go well beyond copying.
I am assuming you entered in the appropriate IP address, and login information. I recall that this plugin works erratically. A few times, I abandoned it entirely, only to have the cameras mysteriously resurface at a later date. It may take some fiddling, but doing so assumes that the theory has some basis. Hopefully someone else has some input.