In SX Microcontrollers, SX/B Compiler and SX-Key Tool, william wrote:

Seems like current issue in SX-Key where if you plug in the SX-Key without 1st switching off power to the board, 
the SX-Key might go into a high current mode. ( more than 150 mA).

Bean can testify to this, he had one dead SX-Key due to this.

When the SX-Key goes into high current mode, programming will fail with the message unable to detect SX-Key.

If you get such a message, it is advisable to quickly switch off the power and try again a few seconds later.

I noticed that the current draw of the SX-Key (when in high current mode) is so large that the un-regulated voltage ( before going into the regulator ) drops in such a way that you can clearly see the Power LED dim significantly. ( its a good idea to have a power led ).  This dimming is also a good warning indication to quickly switch off power.

I also noticed that if the regulator and filtering capacitors are very near the SX, ( for example in a very small board), 
the SX-Key is unlikely to latch into this "high current mode" even if power is not switched off when plugging in the SX-Key.

This issue exists in both SX-Key revision E and revision F.
I hope the new USB SX-Key will have a current limiter......

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