The most common reason you might have trouble with adding a new stock that the club has bought will be if program has added the stock as an inactive security.

To double-check:
Click Securities on the left hand side of the club accounting window.

If you have already tried to add the new stock once, click the Show Inactives box at the bottom of the Club Accounting window. If you have successfully added the stock, it will show up in the list with a * next to its name. This is normal.

Once you have confirmed that the stock is listed there, you can enter a transaction using that stock. Just remember that for the first transaction, you will need to put a check mark in the Show Inactives box in order for the stock to show up as usable.

If you haven't already tried to add the new stock, click Add New.
In the new window that comes up, fill in the details, and click OK.