CARD ALREADY DEALT
You should first of all check that the deck is not faulty. There has either been a misread of the bottom card in the hopper, or an earlier card, if the deck is correct.

The deck (or at least the card) should be replaced if the same card gives the same card already dealt message repeatedly. 

You are advised to read the service instruction and/or email a Report Problem via the System menu if you get this error message randomly on several deals in each set.

FLUSH
Flush will fill the board with 52 cards, but note that that will not solve the problem. You will have a fouled deck in the board, c.f. a separate page on the subject.

RETRY
A safer way going forward is to put  the distributed cards back into THE BOTTOM OF the hopper. Then click outside the error message and insert the board anew to redo. 

SHORT DECK
There will be a special kind of Card already dealt when there is a card missing in the deck. The message tells which card to look for.