Says: Cannot exceed 9999999.99

This seems like a bug. I should be able to enter much bigger numbers. I need decimal(11,2) not decimal(9,2)

this impacts 1e on 1099-b as well!

Annnnnnnnnnnnnnnnd it also impacts:

Total adjustments to gain (or loss)

on the same screen. 

If you have a number that is $10,000,000 or greater.  The workaround is to split the amount.

Example:  You have a $18,000,000 sale, and your cost basis is $12,000,000.

Split this entry into two parts.  Enter $9,000,000 for the sale twice, and $6,000,000 for the cost basis twice.

This works for the IRS because they are only concerned with matching the total.