Can anyone explain this to me?  I have a keyboard connected to the MIDI In and Out on my Focusrite.  If I delete the AUD.INI and TTSSEQ.INI files before opening Bandlab Cakewalk (or SPLAT) and then select Focusrite MIDI as a MIDI Input and MIDI Output in Preferences, the keyboard works fine - MIDI in and out notes and other events are transmitted just fine.  But if I close Cakewalk and then re-open, the Focusrite MIDI Input and Output still show up and are checked in Preferences, but playing a note does nothing. Every single time, I must close Cakewalk, delete AUD.INI and TTSSEQ.INI, re-open Cakewalk, and select the Focusrite MIDI In and Out again. It never works without doing this.  What is going on??

Could be a USB port problem (Especially if it's connected to USB3).  Try a different USB2 port.
 
Are you connected to the 2i4 MIDI in/out ports?  If so, what MIDI interface?

JonD
Could be a USB port problem (Especially if it's connected to USB3).  Try a different USB2 port.
 

The Focusrite and keyboard are connected to each other with MIDI cables, not USB.  Though of course the Focusrite is a USB interface and IS connected to the computer via USB to a USB 3.0 port.  It does not work well connected to USB 2.0 - not well enough to use.

Possibly your not selecting it in the track inspector boxes. 
You might want to go through the Part II of my tutorial where I explain how to set up a controller. 
Here's a few pictures from the tutorial. 

smoddelm
.... of course the Focusrite is a USB interface and IS connected to the computer via USB to a USB 3.0 port.  It does not work well connected to USB 2.0 - not well enough to use.

The 2i4 is a USB2 device and should work best with a USB2 port.  If it were me, I'd try all available USB2 ports before ruling them out and using USB3.

JonD
Could be a USB port problem (Especially if it's connected to USB3).  Try a different USB2 port.
 
Are you connected to the 2i4 MIDI in/out ports?  If so, what MIDI interface?

When I first got it, I had it connected to a USB2 port and it was glitchy like crazy.  Performance (excluding this issue) has been flawless since connecting to a USB3 port.  I just now tried it with a USB2 port again and it crackled and popped in several places within 5 seconds of starting playback in an open project.  Even though the manufacturer says this: https://support.focusrite...69-USB-2-0-vs-USB-3-0
 
I have the 2i4 MIDI In and Outs connected to the MIDI In and Out ports of a GAIA SH-01.  As I said, it works fine if I first delete AUD.INI and TTSSEQ.INI.  But every time I restart Cakewalk (or SPLAT) without again deleting those files, the keyboard no longer sends anything to Cakewalk.  Notes don't play, etc.

smoddelm

JonD
Could be a USB port problem (Especially if it's connected to USB3).  Try a different USB2 port.
 

The Focusrite and keyboard are connected to each other with MIDI cables, not USB.  Though of course the Focusrite is a USB interface and IS connected to the computer via USB to a USB 3.0 port.  It does not work well connected to USB 2.0 - not well enough to use.

 What OS are you using? 
 Are you using a 1st gen Scarlett or 2sd gen? Big difference.
 If you are using a 1st gen on Win 10, check with Focusrite to see if there was a driver update, and ONLY use the 1st gen Focusrite Control software unless otherwise suggested by FOCUSRITE. . Don't take anyone else's suggestions for it
 
If you are using a gen 2 use the gen 2 Focusrite Control. Don't take anyone else's suggestions for it.
 Second gen 2 Scarletts have digitally controls preamps, and overload protection across all I/O.
If it detects any overly high or sharp peaks for even a millisec. it will disconnect for a second or 2 and or shut down all I/O completely until you shut down and restart it.
 YES, a high enough audio peak/voltage surge can and will disconnect your MIDI ports, and so will not having enough buss power coming through from your computer to power everything, the unit itself, audio with 48 volt phantom power to power condenser mics which gen 2's digitally controlled mic preamps analyze and adjust impedance for, and voltage regulation adjusts for extra power needed for MIDI I/O transmit/receive, input monitoring, can each add up and build up to stress levels, especially on laptops with tiny wall wart type power supplies.
 You can easily and cheaply solve that problem with a powered USB hub, just make sure it's a powered USB 2 hub.
and your Scarlett will be happy.
 
"THERE ARE NO BETTER DRIVERS FOR FOCUSRITE INTERFACES THAN FOCUSRITE ASIO DRIVERS!"
As there are no better drivers for any audio interface other than the ASIO drivers that shipped, updated and designed by the manufacturer.
 
 The first driver version release for Scarlett Gen 2 new Focusrite Control suggested using USB 3 but ONLY if you had problems connecting to USB 2, OR install (roll back) and use the older GUI version of Focusrite Control over the newer drivers if simply plugging into USB 3 didn't work.
 The only thing a Scarlett gen 2 hates more that USB 3 is ASIO4ALL.
 
 That issue was fixed with the second version release and Focusrite issued a warning to ONLY run Gen 2 on USB 2 port, and several bugs that cropped up on certain systems have been fixed along the way issued with several updates.
 
 Make sure you are using the Red high quality USB cable that shipped from Focusrite or reasonable "high quality" equivalent with no filter/chokes on it.
 
 Make sure you are running the latest Focusrite Control 2.3.4