matthias65451,
I guess it depends on how badly you want to solve the problem you have.
Yes it may be something that not quite right in your particular setup, or perhaps a combination of Avast and some other software that maybe a lot of us are not running. The more specific information you can provide, the more chance there is of someone being able to suggest a solution.
Exactly what version of Avast do you have - generically "the newest" is Avast5, but there are a number of different versions and builds of that. Also specifically what other programs have functions in your Windows Explorer context menu.
Other items that may be relevant are what AV software did you have before you installed this version of Avast and exactly how did you go about uninstalling the old one, and what other "resident" security programs, antimalware, AV, firewall do you have installed.