new guy here and so far I found CHDK very useful and fun to use!
I was having some problems using the ver.req file to get find out my powershot a720 firmware version by RENAMING a .txt file to ver.req (giving me the file ver.req.txt), trying all the combinations with s, caps on... until I tried CHANGING the TYPE of file from .txt to .req (giving me ver.req without the .txt). Now it works! (Simply right click on the file and choose change type, in the box that says what type of file it is, write .req).
Hope this helps others having the same problem!