Hi Beatus, welcome to the forum
I have the same setup as you (Win 7 64) and the vpsupd.exe download works as it should (I can see it open and it tells me that it my database is up to date.
I used this link to the file:
http://files.avast.com/iavs5x/vpsupd.exe(available from the website)
So I tried updating the virus definitions by downloading the executable file (vpsupd.exe) available under "Support, downloads, updates" from another location
Do you mean that you downloaded it from a different machine?
It may be that the download is providing the version correct for that machine, rather than the one that you want. (Not sure if there are two different versions provided)
I will try and test it by downloading it on a 32 bit system (when I can) and transferring it over, to see if I can replicate.
Scott