I have downloaded the 7z archive, but there is only diskboot.bin and not ps.fi2 . It's enought to overwrite the diskboot.bin i have on the card?
If you have a CHDK 1.1 release installed on the card, then you only need the new diskboot. Otherwise you need to overwrite the modules too. Note that you need to start CHDK with the bootable card method for the test version to work.
p.s. Could the problem be due to ? With brief shutter time i have never had a problem.
Many things can influence how fast the camera's internal image counter increases, dark frame subtraction might be one.
And a word of warning (don't know whether this applies to you, just in case): never mix up CHDK 1.1 and 1.2 installations, if you switch between them, always install the whole content of the release archive.