Problem solved. Thanks I use this:
Starting with the 400.vps, version 100328-1, one of it’s internal block reached the inner limit 33554432 bytes. It’s a kernel variable which
is (quite artificially) limiting the maximum size of any SHM memory block - and 33554432 was a default for some kernels.

Solution? Set the limit to higher values (as root):

sysctl -w kernel.shmmax=128000000
OR
echo 128000000 >/proc/sys/kernel/shmmax

Place those lines to /etc/init.d/rcS or equivalent file (it’s distribution-specific a bit - see /etc/inittab, the sysinit runlevel) to have them set automatically (just after boot).

I just used sudo from the terminal and it worked. Avast now runs. Wonder why Avast does not recommend this in the install? If I had not used Avast previously in “Windoze” I would have quickly moved on.