I have an iPaq running Windows Mobile 2003 SE. The above error was something I’ve seen when I tried installing SkyPE for PocketPC on it.
It appears that SkyPE have decided to sign cab files, according to some new (and pretty unexplained) concept of MS, disregarding any existing non-WinXP or non-ActiveSync4.2 users (and I am a member of these two groups).
The solution was found in SkyPE official forum, in an unofficial post (as most of them seem to be) right here.
The code supplied actually works, and I will consider using variations of it on any future signed cab file I might encounter. I hope it will help… 🙂