Our church has replaced a failing Roland XP50 (nine years old) with a WK3500 a few months ago which I am slowly coming to grips with thanks to Jim and Stephen's sites, you guys are Legends.
Q1: I have tried to purchase smartmedia cards here in Country Australia and been informed that they will soon be out of production and are being replaced by SD cards, which are not compatible with WK series. Any truth in this?
Q2: Roland XP50 had a PANIC button that would stop "stuck" notes (ones that keep sounding after song had finished). Only way I have found to stop these on WK3500 is to press DEMO and then STOP buttons.

Usually, calling up a new program or performance will stop a stuck note. It may not be faster or better that the way you do it now. Stuck notes hardly ever happent to me unless I get "itchy fingers" and push too many buttons too fast.

I've pushed my Casio quite hard and haven't experienced any stuck notes. Check the bottom of the board to see if it's a refurb. My first WK-3500 was a refurb, and it was DOA. The power turned on, but nothing after that. Just a blank blue screen.

Squeak

Sorry I did not explain very well. The problem is when I play a MIDI file that I have downloaded off the internet, not when I am actually playing on the keys. The 'stuck' note I am refering to is during playback of a MIDI file an organ sound, for example, will continue to sound even after the tune has finished. It appears to be no 'note off?' data instruction.



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It sounds like you have already diagnosed the real problem. You should be able to fix that yourself in a MIDI sequencer by adding the note off if it is missing. Probably even just deleting and reinserting the last note will fix the problem.