Doubling of all chat and IM dialogue

Can anyone advise about this problem. It has been persisting over the last four days, before that, everything was normal.
All my IM and chat dialogue are doubled. Everything appears as a double, example:
Say blah blah
Say blah blah
I have NO wireless technology on the computer I am using.
I have done the following:
Cleaned cache on both SL and my computer hard disk
Two clean installs of the SL software
Checked with my ISP that download and bandwidth speeds are as they should be.
Packet loss is at 0.0% Bandwidth approx 350 to 480kpbs
Logged out and in countless numbers of time
Switched off modem and routers and reconnected.
Someone provided me with a De-Echo object, which I attached to my AV and attempted to use channel 1 as a work around. Rather than doubled lines of writing, no writing appeared, even in sims that allowed scripting.
Spoken with SL live help on five separate occasions. They could not provide a fix for the problem.
Am still waiting for a reply to my email to SL technical support.
Any advice would be appreciated.

Have you tried turning off chat logging? See if that works.

Thank you for the reply. I don't have chat logging enabled.
The interesting thing is, that the dialogue only doubles on certain sims.
In others, it is completely okay and works fine.

The downside is that the double happens on the sim I live in and all of the ones that I spend the most time in.

If I stay in relatively desterted sims, there's no problem.

I could either be SL's first mime or first recluse.

as its sim based problem, it must have something to do with the client interacting with the server OS. Alternatively, you have a twin trying to talk to you from your client you never knew about.... spookyyyy