I'm having trouble with the USB drivers (or the USB port) on Mac OS X. What can I do?

Verify the following 3 points:

1. Make sure you have enough disk space.
2. Manually remove the driver, and re-install.
3. Enforce the proper ownership and permissions on the driver files.

In detail:

1. Make sure you have enough disk space:

The USB driver needs a lot of free space on the disk. We do not have an accurate measure, but 100MByte would cover it. If you have less than 100MByte of free disk space, this might be the cause. Try to free up some disk space and re-install the driver.

2. Manually remove the driver, and re-install.

a. Bring up a terminal:

Appliction->Utilities->Terminal

b. Remove the kext cache files (may not be present):

sudo rm /System/Library/Caches/com.apple.kernelcaches/kernelcache.* (you will be asked for your password)

c. Remove the kext files:

sudo rm -rf /System/Library/Extensions/FTDIUSBSerialDriver.kext

d. Remove the receipts (may not be present):

sudo rm -rf /Library/Receipts/FTDIUSBSerialDriver.pkg

sudo rm -rf /Library/Receipts/FTDIUSBSerialDriver.kext

e. Remove the startup scripts (may not be present):

sudo rm -rf /Library/StartupItems/FTDIReEnumerate

At this point the driver should be gone. I'm not sure it's necessary, but I would reboot now.

After rebooting, check with your System Profiler to make sure it's gone.

Download a fresh version of the driver from our website (perhaps your local copy is somehow corrupted), unpack file, and double-click on the .pkg file to install the driver as described in the user's guide. NOTE: you can also download the latest driver from the FTDI VCP drivers page (it's the official page of the usb chip manufacturer) and install FTDI's Mac OS X Driver.

Follow the installation procedure and allow it to reboot.

3. Enforce the proper ownership and permissions on the driver files.

a. Bring up a terminal:

Appliction->Utilities->Terminal

b. Change your working directory to the driver directory:

cd /System/Library/Extensions

c. Change the owner for all files and directories of this driver to root:

sudo chown -R root FTDIUSBSerialDriver.kext

d. Change the group for all files and directories of this driver to wheel:

sudo chgrp -R wheel FTDIUSBSerialDriver.kext

e. Change permissions for all files to 644:

sudo find FTDIUSBSerialDriver.kext -type f -exec chmod 644 {} \;

f. Change permissions for all directories to 755:

sudo find FTDIUSBSerialDriver.kext -type d -exec chmod 755 {} \;