Fix error logging format string mangled by a bogus comma.

Fix error logging format string mangled by a bogus comma.

A format string was split over two lines, with the second line
containing the format specifier that prints the channel name.  A comma
was incorrectly appended to the first line, causing the format specifier
substring to become an argument string.  Since no format specifiers
remain in the main string, the logger does not format any arguments.
Remove the bogus comma to fix that.