Solved!
I spent the whole weekend trying out everything - 6 new CF-installs, freebsd-crash-course ;) … no success!
Past Midnight, i was near giving up, every single package installed perfectly. What happend?
Finally i found the problem: We have a 3 Mbit-satellite-connection with 700ms-PING and heavy throtteling, so most of the time we only get 64 kbit/s. But we have a Freezone from Midnight until 6.00 am, where Bandwith and download-volume is not limited. The reason why the installation was only succussful after midnight, was definitely the slow internet-connection during the day. Although the package download completed (slow, but complete!) the final install-check failed because of the slow connection. I don´t know how this could be, but i am sure, that this was the reason.
Have a nice week, greetings from the the ecovillage of sieben linden,
Sascha
p.s.: now i have squid/squidguard and freeradius running well on 2.0 on an alix-board with 8gb SLC-CF-Card. I will see how long the CF-Card will run, some experts told me, the new CF-slc-cards should run for many years. Backup, wait and see :)