ashBase.dll is an integral part of avast!. If it is not present on the target machine, I strongly recommend reinstalling the program: uninstall > boot > install again > boot
In case of missing avast! file you can also use “Repair” option of avast! setup - go to Control Panel and use “Add/Remove Program” applet. In its dialog select “avast! antivirus” and choose click “change/remove” button.
Maybe these forums could help:
http://forum.avast.com/index.php?board=2;action=display;threadid=2462
http://forum.avast.com/index.php?board=2;action=display;threadid=1894
Wellcome on board. I think you does not have a trojan, just an installation problem. By the way, which is your operational system? Do you have any other antivirus installed in your computer?