[Elecraft] Need "Error TxF" help

[n5qq61 at gmail.com]

Having trouble with one of my three K3's, sn 02138, generating ERROR
TXF. Radio had 3.97 firmware, which I updated to latest version as of
this morning.
CW transmissions are fine but any attempt at SSB transmissions results
in ERROR TXF. Don't know how long it has been like this as I rarely
get on SSB.
Radio has the stock 5 pole 2.7 filter in FL1, plus CW filters in other
slots, but no AM or FM filters.
FLtx Sb is set to FL1.
FL1 is enabled ON.
FL1 BW is 2.7.
FL1 freq is -0.78.
I have a spare (new) 2.7 filter that I even swapped with the
previously installed one, plus I changed the filter position (and
reset the configuration as required).
I checked all above via radio CONFIG MENU on screen, and also with the
K3 UTILITY.
I tried it with VOX and without. I tried it with tapping XMIT button.
I tried it with MIC plugged in front and in back, and with no mic
plugged in at all. (MIC is Heil Proset.)
I have checked and re-checked the filter settings and all seems to
coincide properly unless it is just a "forest4trees" thing.
I did try the above on 160,80,40,20,15 and 10m.

What did I miss?
Help??

Ron
N5QQ