I expect that it's telling you that you haven't reported enough "shares available for sale" for the number of shares you actually sold. That's usually the result of having multiple sales out of a lot, (e.g., reporting both the sale of shares "for taxes" and the sale of shares "for cash"), and including in your input on the "Enter Vesting (or Release) Information" page a number in the "Shares Withheld (Traded) to Pay Taxes" box. The only thing entering a number in that "for taxes" box does is that number is subtracted from the number of shares you reported as vested to come to a "shares available for sale" figure.
So, for example you reported the sale of 10 shares for taxes and entered 10 shares vested and 10 shares were sold for taxes you'd end up with 0 shares available for sale.
Try going back through the RSU step by step interview and blanking out any numbers in the "for taxes" boxes and see if that fixes things.
Tom Young
