My wife and I both have Samsung Captivates. After we updated to 2.3.5 using Samsung Kies mini we started seeing tethering manager forced close messages when we charge the phone either through a power outlet or an usb port. I saw the suggestion of resetting the phone to factory settings as a fix but I did not want to go through the trouble, as least not yet.
I was concerned that with this tethering issue, I would not be able to connect to the PC. So I reconnected to Samsung Kies mini on my laptop using the usb cable. Samsung Kies mini went through the motion of checking for updates and reported that there was no update. I then exited my Kies mini connection on my phone using the HOME key. After this exercise, my phone no long exhibit the tethering manager forced close issue when the usb cable is plugged in for charging. I went through the same process with my wife's phone, and now it is fine also. I shall give it a few days to see if the problem returns.
In trying to rationalize why this is working for me, the only thing I can think of is that when I updated the firmware, instead of existing Kies mini from the phone using the HOME key, I used the 'back' key instead. The instruction on the phone clearly says HOME key.