do start and run regedit
then open
HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Explorer \ FileExts \ .wix \ OpenWithList
cancel all the items in this window except the (default) REG_SZ (value non setted) line.. then restart the pc and the icons will be set to default again..
anyway as the others said this doesn't cause any kind of error for your client