Thank you for your response.
I have installed Glims 1b27 - no change in behavior. (I had not received notification of this update. Perhaps because I had asked for stable releases only.)
My Plugins are:
Flip4Mac Windows Media Plugin 2.3.6
Flip4Mac Windows Media Web Plugin 2.3.6
Garmin Communicaton 126.96.36.199
Google Earth (for google earth 188.8.131.528)
iPhotoPhotocast (iphoto 6)
Java Plug-in 2 for NPAPI Browsers
ShockwaveFlash 10.0.r45 (from ClickToFlash.webplugin)
SilverLight Plugin 4.0.51204.0
Switchable Java Plug-in for WebKit
Web Kit EPPEX Contents Plugin
Most of these plugins have been installed for at least several months. Java is the most recent update (version 13.4 from March 8, 2011).
One "add-on" that isn't reported in the Safari plugins list or extensions preferences is rapport by Trusteer.
I tried to eliminate other add-ons to find this problem without success. I used the system profiler to look for events that might relate chronologically with the start of this problem. I stumbled on an Apple Support discussion about rapport. It sounded similar, so I removed rapport from my system and the errors stopped.
I don'd know if Trusteer is working on a fix, but I sent them a synopsis of this problem.
I had the same problem, excessive errors in the System Log. I spent a couple of hours with Trusteer support this week and we traced it to the ClickToFlash Safari "add-on".
The messages stop if ClickToFlash is disabled. However, I'm not going to give up on ClickToFlash so have uninstalled Rapport.
Hopefully they will fix the ClickToFlash interaction problem sometime in the future.