Sounds like your doing all the right things, but who knows what Windows is
still doing in the background. It's amazing that WriteLog works as well as
it does as a keyer. I'm considering purchasing the W5XD Multi+ keyer that
takes CW generation away from the CPU and does it externally. FWIW, with
just WriteLog (no external keyer), all background programs running, Packet,
and Rig Control all running this weekend, I had no CW generation problems
this weekend on a 166MHz Pentium.
Perhaps N5NA's suggestion will cure your problem. Otherwise, one other thing
you might want to check for is mild RF in the shack. A little RF, not
serious enough to cause things to totally lock up, but enough to cause
intermittent problems, can cause erratic CW as you've experienced.
73, Bob - W3YY