For everyone else searching here are a few options.[br]
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One is to use canned air to blow between the keys. The other (try at your own risk) is to smack the back of the keyboard. Finally you can undo all screws on the back and carefully remove any dust or debris, this is much easier and safer after you undo the ribbon cables attaching the two halves. With those carefully disconnected you can shake the half with the keybed to try and loose any dust or debris under the keys.
This issue can be caused by deteriorating rubber pads under the keys or dirty contacts. One solution may be to clean the contacts for the keys using alcohol wipes or to replace the rubber pads.