[Elecraft] K3 ERR KEY - Continuous Keying

[Bud Governale, W3LL]

My K3 display shows ERR KEY when I turn it on. It's been working flawlessly until now and no recent changes have been 
made.

1.    No programs are running on the computer. ERR Key is displayed on the K3
2.    If I shut down the computer the ERR Key turns off partway thru the "Windows is Shutting Down" screen.
3.    If I turn on the computer with the K3 on, it keys the transmitter a few times then it keys on continuously after 
windows comes up.
4.    I disconnected both the RS232 and ACCY cables from the K3 but surprisingly the K3 remained keyed with the same 
symptoms.

5.    I disconnected the Line Out cable from the K3 and it unkeyed. However, it would periodically/intermittently key 
for about half a second on its own.
6.    I reconnected the Line Out and the K3 again keyed continuously.
7.    I disconnected the Line In cable from the K3 and the K3 unkeyed. However, it would periodically key for about half 
a second on its own.
8.    I checked both Line In and line Out cables for continuity or shorts. Both are OK.
9.    I checked the sound card for functionality using a second radio. It works properly for both Line In and Line Out.
10.  Both Line In and Line Out cables are stereo cables.
11.  If the K3 is on when windows starts up it goes into key down mode. If I start windows with the K3 off and then turn 
the K3 on the K3 displays the ERR Key diagnostic.

I don't understand what Line Out or Line In has to do with keying the transmitter.

Any suggestions on what happened and how to fix it? Until now all has been perfect.

73,

Bud W3LL
w3ll at arrl.net