Assume you mean errors.txt in the logs folder? It's empty.
I'm talking about the file you've set in, $PROGRAM_ERROR_LOG - if that variable is set correctly, it should point to the location of the error log. You shouldn't have to (and really, shouldn't) create this file yourself.
It's suspicious that there's absolutely nothing in it. I would remove the file, make sure the directory gives enough permissions for a new file to be written in there and try a test mailing again. If the file doesn't regenerate itself, something's up path-wise or permission wise. If the file does regenerate itself, but without any errors, color me surprised - even on completely successful runs, warnings are logged in that file.