applescript error message not in UTF8 format?

I have a script that processes mail messages. Every now and then I get an error along the lines of:

-1728: Can't get 'class mssg' id 65163 of 'class mbxp' "Sent Messages" of 'class mact' "mymailacc"

The errors are written to a log file.

In the log file, every tick mark (') has a weird character in it's place. When I open the log file, I get a warning that the text is not in UTF8 format.

Am I supposed to do something with the error message in the script before logging it?

Thanks,

Craig.