The Problem:

After installing Cisco’s Mac VPN Client and launching the application, you get the message:

Error 51: Unable to communicate with the VPN subsystem.  Please make sure that you have at least one network interface that is currently active and has an IP address and start this application again.

The Solution:

If you just bought a new MacBook Pro (17-inch, Early 2011), MacBook Pro (15-inch, Early 2011), MacBook Pro (13-inch, Early 2011), or Mac Pro (Mid 2010), your system will – by default – load with Apple’s 64-bit kernel (Apple 1).  This prevents you from launching certain 32-bit applications.  In order to use your VPN, you will have to switch your boot kernel to 32-bit:

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The Problem:

MacBook Pro speakers are not functioning.  Headphones work fine but, when they are unplugged, a red LED turns on inside the headphone port.




The Solution:

You are using a non-Apple headphone set that has (or had) a gold coating on the jack.  The coating has rubbed off inside the port and clogged the mechanism that switches output between headphone and speakers.

Using the same headphone jack, repeatedly insert the headphone jack until the light turns off.