Depending on what driver and firmware you are running with your 1818, this is to be expected.
AudioBox VSL Software Discontinuation Notice
Effective September 29, 2015, PreSonus is discontinuing development on the AudioBox Virtual StudioLive (VSL) software for the AudioBox VSL-series. We are not discontinuing the hardware itself, this is just for the software control panel that comes with the interface.
Changes in the Mac OS X operating system (OS X 10.11 El Capitan) prevent the VSL control panel from functioning as designed. Fortunately the AudioBox 1818VSL, 44VSL and 22VSL are fully class-compliant Core Audio devices and can be used on Mac OS X without the AudioBox VSL software installed.
By using the built in Audio MIDI Setup Utility found in the Applications / Utilities folder, all inputs and outputs can be managed manually within the operating system.
By removing the VSL software, you can take full control of all of your Inputs and Outputs by managing them in your Digital Audio Workstation software.
Due to the discontinuation of the VSL Software for the Mac OS X platform, PreSonus will no longer be continuing development of VSL Software for the AudioBox VSL Series for the PC Platform.
In August of 2016 we released Universal Control 1.8 which supports the AudioBox VSL series interfaces. It does not contain the VSL Software. However it will allow you to uninstall the non-functioning AudioBox VSL 1.3 software, and it will allow you to update the firmware to the latest supported version.
Universal Control 1.8 (or higher) is available on the download page for:
NOTE: AudioBox 1818VSL Remote for iPad will continue to function for previously supported operating systems where AudioBox VSL software is supported.
Please Note: With this recent change in El Capitan, AudioBox VSL users will not see the "Z" or Zero Latency feature within Studio One.
We've also created some tutorials to assist with getting your AudioBox VSL interface up and running without AudioBox VSL Software, including learning about default routing of the inputs and outputs and how to send audio to your headphones.
Lastly, if you still need to use the AudioBox 1.3 software, you can always opt to downgrade to a previously supported operating system where that software still works. We no longer provide support for AudioBox VSL software, any issues will need to be discussed in the AudioBox VSL Community forums.