Sorry I'm not an avast server edition user, so I'm not sure how this works with the server edition, but what is common in the avast 4 Home/Pro is the avast icon, ashDisp.exe (or possibly aswDisp in the server edition) is kiled by other security software that monitors startup entries.
What other security based software do you have that might block new startup entries, e.g. Spybot S&D (TeaTimer), AdAware (AdWatch), SpySweeper, Spyware Doctor (StartUpGuard), PrevX, WinPatrol, ProcessGuard, etc. (excuse the various desktop versions but there are likely to be server versions for some or others) ?