When HBC beta 9 came out, many people were getting problems when they tried to boot certain apps. The error said something about "This is not a valid Wii Application".
Its not a coincidence that all apps that stopped working are elf files. This is caused by the bad compiling of an older DevkitPPC release (Newer versions will produce valid elf files).
If you still want to use those old elf files, you can use this handy tool to convert them to dol files.

Required:
* A computer

Links:
* ELF to DOL converter: windows, mac, linux

Guide:

Computer ----------------------

1. Download the elf to dol converter. Now extract all files to the apps folder on the SD card.

2. Before we run the application, be sure to check following things:

• The elf must be placed in any folder in the apps folder.
• It MUST be named boot.elf
• If there is a boot.dol in the same folder as the boot.elf it will be overwritten
• Any valid (working) elf will stop working if it is converted to dol

If you are sure you can safely run the app, run elf-dol_converter.bat and wait. (Note: just follow instructions of the included readme)
Thats all!