If there is no picture on the SD card at all, then ...
A never expected exception on Your SD-cards...

In short: make sure you don't use a Canon Basic script and CHDK at the same time.
My card with dual boot:
SD-lock open runs CBasic, locked boots CHDK. If the 1st key != "set", CHDK seems undisturbed, else an existing expand.m is executed.
If I use it locked on other cam, it tries to load wrong diskboot.bin...

Edit2: Tried both together on M100 : How long "wifi" is pressed matters.
Who gets the <ALT> ?? Lucky timing leads to different menues.
At least Cbasic & Ubasic could coexist...
