***** POSSIBLE WORKAROUND *****
When I upgraded to YW!E 4.5 I had the same problems others here stated. While leaving the Yahoo Widget engine running, I closed SimpleMonitor and reinstalled it from the Yahoo Widget website. The version of SimpleMonitor hasn't changed, so I'm guessing that SimpleMonitor and Yahoo Widget engine needed to reset some internal settings.
Excellent widget! Simple, shows the important stuff, not hard to setup. The IP address it shows is even your WAN side widget if you have a router. VERY GOOD!
The preferences ask for bandwidth in terms of kb/s (kilobits per second), but is in fact scaled to kB/s (kilobytes per second). 1 Byte = 8 Bits. The scaling is thus shown incorrectly if you enter the bandwidth limits in kb/s.