My Presonus AudioBox1818 VSL is recording and playing back ok on my 32 bit X1 Producer-Expanded(Vista!). On my 64 bit OS - the same DAW: the Presonus Input Drivers, and Output Drivers show up on my Edit, Preferences, Audio Device menu( I have downloaded the recent 32/64 driver). The Inputs are showing on my Track Inputs....  But no signal on record, and when I attempt to playback audio - error message pops up: "Unable to open audio playback devise. Devise may not support current project audio format or may be in use." 
 
As a test, the interface is recognized and works with Studio One (Presonus) and Harrison Mixbus - But I really want it to work with my X1. Tweaking around with the AudioBox mixer that downloads with the driver, does nothing...  

You need to post some system specs.
You say "On my 64 bit OS - the same DAW"
Is this a dual boot 32/64 system, or 64 bit OS running Sonar x86 (32 bit) and Sonar x64?
 
Tom

Looking on the download page for the 1818VSL v1.3 does not support Vista. The last driver which mentions Vista support is v1.2.1.

I have the PreSonus 22VSL, purchased because of the integrated fx (which I wanted for confidence reverb)
 
With the first driver set, it only worked in WDM mode.
With the driver update it then worked in ASIO mode but something else did not work anymore, I forget what.
There has never been another update, yet many people reported the same issues I had.
 
It is now back in the box in the cellar.

I have a 44VSL which I used in X1, X2, X3, Mixbus 2.5, Mixbus 3.0 and Platinum.
The only Problem I've ever had was when I tried to upgrade to Windows 10. Sonar will not work here in Win 10.
Mixbus does. I've never been sure, but I suspect the problem was with the 44VSL.
 

@clintmartin: That's the big brother of mine.
Do you use it in ASIO or WDM?

ASIO
 

H'm. New 1.3 drivers, dated 21. July, 2014.
Maybe I should get it out of the cellar and try again.
Thanks!

Sorry for the lack of clarity on my original post - lets just stick with the 64 bit system where it does not work: it is a 64 bit only Windows 7, Service Pack 1. The  PreSonus driver is for 64 or 32 - when I installed it, and it asked checked 64. Here is the driver info: 
AudioBox 1818VSL v1.3 - PC
AudioBox VSL - PC - Control Panel with Monitor Mixer and Driver for Windows 7 SP1, Windows 8.1, & Windows 10
(32-bit and 64-bit* compatibility for all listed Windows versions).

This knowledge base link on Cakewalk was available, and I thought it would help - but refers to the Universal Control which I don't have - should not matter though since I got it to work on my 32 bit desktop/Sonar version:
 
http://www.cakewalk.com/Support/Knowledge-Base/2007013386/Focusrite-and-PreSonus-Interface-Routing-Setup