Hi,
The 2.3.5.5 version of mojoPortal went live in the web app gallery last night but apparently they made some mistake in posting it because I get the same error about it failing signature verification.
I've contacted Microsoft about the problem so hopefully it will get fixed later today.
The verification only is done when installing from the gallery, they check against a checksum to make sure the file that was downloaded matches the checksum of the file that I submitted to the gallery. When you install a package directly from IIS it does not do this, it is only needed for the gallery.
I'm sure I submitted the correct checksum for the file I submitted so it must have been a mistake on their end, in any case I'm sure they will help fix it, though they are on the west coast so it may be later in the day before the get to it.
Best,
Joe