The use of wildcards can be of use as well, just make sure that the path is actually where avast is installed.
Example of paths: C:\Program Files\ can be %PROGRAMFILES% or %PROGRAMDATA% for Win7
The reason that it didn't work is that amwChams.exe isn't in the System Path on computers, unlike executables in the Windows\System32 folder, so when you just type amwChams.exe, it has no idea where to find it.
So, you must actually tell it where to find it first, before running the program.
You can easily tell if a program will run properly or not before putting it in a script by just opening a run box and typing the command. If it says it can't be found, then it's not in the system path, and you'll have to type the full path in the script...