Looks like perhaps this line:

# Stop the timer and print.
if ($db_benchmark) { $t1 = new Benchmark; print "<h6>Processing Time: " . timestr(timediff($t1, $t0)) . "</h6>"; }

In your .cfg file you can comment out the line for benchmarking if you are not using it.

# $db_benchmark = 0;

I think this will stop the error from reporting.

Hope this helps

Unoffical DBMan FAQ
http://webmagic.hypermart.net/dbman/