Repairing is only possible if it is a true virus. With other malware (worms, trojans, spyware, adware and such) the only remedy is to remove the files.
You may want to take a look
HERE for definitions.
As you can see in the virus library (start avast > menu > virus library) Avast can not repair the infected file(s).
I suggest you send it to the virus chest.
When it is there make sure it is indeed malware. (run a online scanner like
JOTTI to scan the chest folder.
If it is indeed malware, and I think it is, delete it from the virus chest.
That should solve the problem.
In addition you may want to read
THIS page for aditional information on how to clean/secure a system.
Let us know if the problem is solved or not. And remember:
There is no need to rush. Take your time. Better slow and safe than fast and still in trouble