Probably nothing, and am I correct in guessing that is measuring the voltage with the cable 'in free space' or without being connected to a PICAXE and download circuit ?
If you explain what problems you are actually having it may be possible to give better advice.
I have found that a cheap logic probe (<A$10) is invaluable in situations like this. You can check the logic levels on the actual PICAXE's SerIn or SerOut pins during the attempted download.
Failing that, all you can do is carefully check your wiring.
A logic probe is so useful in sorting out hardware problems (and checking programme operation at times).
There's a checklist somewhere ( forum search ), but the obvious are - is the board powered up, PICAXE in place and right way round, correct Com Port selected, correct operating frequency chosen ... and have you tried a hard reset ?
Not at all, and the PICAXE is one of the most robust microcontroller chips.
What can destroy it is running off too high voltage, shorting outputs to 0V or putting the chip in the socket the wrong way round.
Are you using a manufacturer supplied board or did you build your own ? You can try to download to it from another PC or try to download to a different PICAXE.