Computer won't recognise Ardweeny serial port / usb modem.

I am a total newbie, just built an Ardweeny. I hooked it to the computer via a Solarbotics USB to TTL adapter, had to install FTDI drivers on my MacBookPro running OSX 10.5.8. After install I was able to connect and upload to the Ardweeny once but now when I connect it I get

"Serial port /dev/tty.usbmodem621 not found. Retry the upload with another serial port?"

I have an Uno as well and it connects no problem.

I have been looking around for a solution but haven't found anything that works. Help me please!!!

Ahhkkk!! FINALLY figured it out - the cable was bunk! It gave power to it but the signal wasn't getting through.