Then I go to the console and type "dumpprivkey <address>" and it responds with "Private key for address <address> is not known".
The function is returned as "private key not found" only when you type the dumpprivkey in console while the wallet is locked. You need to unlock your qt wallet before typing the dumpprivkey in the console. You can unlock your wallet by typing
walletpassphrase "passphrase" [unlock time in sec]
Once after this function has been executed, you can proceed with dumpprivkey [address] which will give you the private key of the address.
Note that regarding tracking of transactions, consider my previous reply on your earlier thread to use the --rescan function.