I am talking about the capital gains report here. I have seen errors on my report provided by ameritrade but I think it's really a freebie from gainskeeper. Maybe it's a trial thing. Not sure if I would get a correct one if I pay gainskeeper.
In terms of statements. I have seen errors on my transaction history not matching up with my statement. I had to talk to support to clear up the problem. But it's no biggy. But you really should check your statement.
Someone I know had $10K taken out from his bank account (not brokerage). It turns out that the bank clerk made a typo on the account number. Scare the crap out of him when he read his bank statement. But luckily he did, on a timely manner and he was able to recover the loss. But if it's a smaller amount, he might not have noticed because no one checks their statement line by line. From now on, I will!