There was an excellent review of Sandisk, on this site, and the related problems, I have the freebie I got with the X5 and mine is Japanese made, so it is fine, so far, but ones made in other countries, I know from what I read, cause untold headaches. It was this review and that which I read on alot of other sites that led me to buy a Lexar 40x CF card with which I have had no problems doing whatever with eg. transfer of files, running apps etc.
From the research I did it seems if you don't know the origins of the Sandisk card they are best avoided and it is better to spend an extra few dollars on a reliable make. Alot of digital camera sites run good reviews on storage cards and one carries a comparison table and if I can find the link I'll post it.
Update: this is the link for CF cards
http://www.dpreview.com/articles/mediacompare/