Thanks for the replies. Wrong choice of words! Shouldn`t have said "blocked" and I do appreciate that it`s Windows that`s actually generating the error boxes but couldn`t understand why turning off Avast`s resident protection cleared the problem, although it`s not throwing up any infection warning as such.
wyrmrider: I had thought of that but it looks like the exclusions option is only for scanning and doesn`t effect resident protection.
DavidR: A conflict of some sort had gone through my mind. I used to run AVG quite happily, but had some difficulty installing their updated version on this machine, (errors during installation. Regretably, I`ve forgotten what they were) although it installed OK on another older PC I have, which is why I uninstalled it and went for Avast. I am also running Spyware Doctor and Threatfire as resident, which are both supposed to be OK and not conflict with anything else but I have exited Spyware Doctor (and stopped the service also) and actually uninstalled Threatfire but I still have the same problem trying to run the two programs mentioned. I`ve had a look at services.msc and there doesn`t appear to be anything untoward there. I`ve gradually shut down stuff in the notification area/tray to the bare minimum and still no joy. I was going to try safe mode when I`ve posted this, but does Avast run?
Tech: I`m not quite sure what you mean about G-Pass. It downloads as a zipped folder and four separate files are extracted to another folder, including the stand-alone executable, which alone is replaced on any upgrade (of which there were quite a few when it first came out!). I moved the folder from my "downloads" folder to the "programs" folder and created a short-cut to the executable. That`s all there is. See attachment. As you can see, the executable icon has changed to the Windows generic and is not would it should be. See second attchment. This is after disabling Avast. I copied the short-cut to the quick-launch bar and that also reverts to the generic quite often but there doesn`t seem to be any pattern there.
The other program`s icon (MakeInstantPlayer) seems to stay as it is, but I still get the error box when I try to run it until I disable Avast`s resident protection. Odd. As far as I can tell, these two are the only ones giving me trouble.