iTunes will only sync purchased songs to iPhone 4 / Unkown error (-50)

Just got a new iPhone 4. got latest firmware and latest version of iTunes. iTunes only seems to be able to sync Purchased AAC tracks to the iPhone. Any tracks that I've ripped from a CD and are in AAC format won't sync and give error "iTunes cannot sync <song> to iPhone. Unkown error (-50).

Any ideas how to fix this?

I've tried once recommendation I found to run a .bat file containing the commands below, but this made no difference.:

regsvr32 /s softpub.dll
regsvr32 /s wintrust.dll
regsvr32 /s dssenh.dll
regsvr32 /s rsaenh.dll
regsvr32 /s gpkcsp.dll
regsvr32 /s sccbase.dll
regsvr32 /s slbcsp.dll
regsvr32 /s mssip32.dll
regsvr32 /s cryptdlg.dll
regsvr32 /s initpki.dll