The baud rate of Tera Term equals to the device?
I have exactly the same problem but here are some more details. I am running Teraterm 4.73. The settings are 9600,n,8,1 with no flow control. The usb dongle is a "prolific" with driver version 220.127.116.11 The problem has occured with various version of Teraterm starting with (I think) 4.59 I can correct the problem by disconnecting and reconnecting to the port. I am running windows 7 64bit. I often run two serial consoles, one with the inbuilt com port and one with the usb dongle. The problem only occurs on the usb when displaying large quantities of text. I have tried several different usb dongles and they all do the same thing. There is no problem when using Putty.
I have the same problem using Prolific chipset and driver version 18.104.22.168, and TeraTerm 4.75.
This didnt happen with Putty, but then Putty kept blue-screening my PC.
I also met same problems. any solution for it?