system
4
open “My Computer”, navigate to the folder where you saved the cleaner to, rightclick the file and select rename

or go Start → run
then enter
ren c:<path/folder_to_Cleaner>\aswclnr.exe c:<path/folder_to_Cleaner>\aswclnr.com
hit Return
or redownload it, and save it from within your browser as blabla.scr or whatever.cmd or clean.pif or helpme.com
etc etc etc…
or, if when opening EXE-files, you get an error message with a specific filename in it
save/overwrite the cleaner as exactly that filename, in the folder where you earlier deleted the infected file from…
Most of this is pretty well explained in the instructions for the cleaner:
http://www.avast.com/eng/avast_cleaner.html
P.S.: If you don’t succeed, doing the above in SafeMode (F8-Boot) could help, too 