You may be trying to set it active before it is ready (which means that Invoke() didn't really work correctly). I also see intermittent errors like this in my code. My way of handling it is to have multiple retry mechanisms: first, invoke the browser in a do-except clause and put another try in the except clause:
</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">do
return FALSE</pre><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">For me, the return value will be used to kill my VM image and restart it. As with your observation, it almost always works the second time. I sometimes see this happening 5 or more times in a row and thus I am really happy to have my recovery mechanism.
In my opinion it is a bug with the extension code that has been around for as long as I've been using SilkTest.