This article is from the ZTerm FAQ, by Les Jones email@example.com with numerous contributions by others.
The characters you've pasted are illegal on the system you're
logged in to. A lengthy explanation follows.
On the Macintosh, all eight bits of a byte are used for characters,
producing 256 possible characters (two to the eighth power is 256).
Internet mail and Usenet newsgroups use only seven bits for text,
producing only 128 possible characters (two to the seventh power is
128). If you use any characters which use the eighth bit, the host
computer ignores the last bit and uses the first seven bits to
determine which character to display.
To avoid illegal characters when composing text for a mainframe,
never use any characters which require pressing the option key.
Also, in your word processor, turn off smart (curly) quotes, which
use the eighth bit. When smart quotes are turned on, the word
"don't" usually becomes "donUt" when pasted to a mainframe. And
I'll bet dollars to donUts you donUt want that to happen.
If you need to upload or paste text files containing illegal eighth
bit characters, process the file with the Zap Gremlins command in
BBEdit Lite (freeware by Richard Siegel).