When you enter the account information and FC tries to process it, it's all done by computer. If the computer link to the bank says the account number is wrong -- then something IS wrong.
It could be a problem with the data you submitted to FC or it could be a problem at your bank.
Check all of the items: account number; routing number for bank and Bank Name.
Go to your account page; click on Direct Deposit; click on View/Change and verify your info. It only shows the last four digits of your account number. But if everything looks good at this level, you need to go back to Support and ask them to tell you how to see the entire account number submitted.
I got this far, but then I clicked on "submit" to see if I could see the full account number and it cancelled out everything that I had put in before -- so if I want to use DD, I will need to resubmit the information.
Not a probem for me: I use PAYPAL. It's easier for me.