Some info from my Lexar SD card supplier:
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I have some good news or at least a good explanation regarding the problems you had with your Dell. I finally was contacted by the head of technical support at Lexar and he explained that indeed a number of their SD cards will not work properly with Dell Axims or Palm Tungstens. Apparently, Lexar is not yet manufacturing and designing their own Secure Digital cards, but are working with other OEMs. These other manufacturers make the cards for Lexar.
More than likely the card you got one with a SanDisk controller. Apparently there is a block of cards with certain serial numbers that have this problem.
This Technical Support fellow was aware of your name and said he had been contacted by Lexar UK and that a replacement card has been sent to you.
It will be one with a different controller inside and it will be fine. Have you received this yet? If they did not ask for the other card back, then consider it an item you can sell on Ebay and get some money for! I hope that this means all will be resolved with the card and the problems you had. In another few months, Lexar will be making their own cards and hopefully they will be sure to work out any bugs before distribution.
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Hope this info helps.
Basically sod Sandisk - and be careful with certain Lexar cards