After installing trixbox and updating the system I could not add new extensions using FreePBX.
Although the solution is quite easy, it took some time to find out. So here it is (I found it in the FreePBX-Forum):
Simply delete all contents in the files /etc/asterisk/vm_general.inc and /etc/asterisk/vm_email.inc. Then perform an amportal restart and everything works fine again.
I wanted to give Asterisk a second chance and thus decided to install trixbox 2.4 on a test machine. This machine is an old IBM Netfinity 5000 (dual Pentium II, only 128 MB memory but a nice SCSI RAID). Unfortunately the installation failed because the system got locked, when the driver for the Adaptec SCSI controller (not the RAID controller) was loaded.
Surprisingly, when I used the "linux" boot command instead of "default", the installation went fine. However, trixbox did not work (freePBX was not installed correctly). So it took me some extra time to find out, that using the "linux" boot mode the wrong installation script was used.
So finally I figured out, that actually trixbox can be installed correctly by using the boot command "linux ks=cdrom:/ks.cfg skipddc". Basically this is the same as using "default", but "default" also includes the "acpi=off" option which causes the problems with the SCSI driver mentioned above.
Sometimes small problems like a wrong boot option can literally take hours to be solved...
Now I am looking forward to get a working Asterisk installation, however there are probably more problems to come as I want to use an ISDN card with mISDN. So it looks that I will be busy with Asterisk for some more hours 