Thanks Pure Blooded, i'm a total newbie with Ubuntu but i really like it a lot.
I have no terminal experience at all though, and by doing as you instructed Avast came back to life, but i made a mistake the first time i did it, and had to repeat the instruction again correctly, but by doing it incorrectly the first time have i caused any further problems?, or by repeating the process correctly the second time, did i then rectify any problems i may have caused?.
What i did was to open a 'terminal window' and typed (it was one zero short at the end, but i hadn't realized yet).....
sudo sysctl -w kernel.shmmax=12800000
....it then asked for my password which i typed in, and then this line appeared....
kernel.shmmax = 12800000
.....it's then i notice the figure was short by a zero , i then closed the 'Terminal window' and gave Avast a go again with no luck, the same window opened " An error occured in avast! engine: Invalid argument", i clicked 'Ok' to closed it
I again opened a Terminal window and repeated above, this time to the correct 128000000 value, it did not request my password this time and just displayed below...
kernel.shmmax = 128000000
...i then closed the Terminal window and tried to open Avast again, this time it opened and so i'm assuming it has been changed correctly, and that this change is permanent.
I would be very grateful if you, or any forum member could confirm if i've left everything ok on the system, thanks for any help.