Yes, I've had this issue as well. I set the ecrypted network as a default profile to be auto-managed by Access Connections (always on when the router is in range). When returning from standby or hibernate, it fails connection about 1/3 of the time. On restart, it fails only 1/10 or so. I just right-click the Access Connections task-bar icon and open Access Connections. Click Connect & it works. Not sure why, but this work around works when needed.
Others have recommended ditching AC, but I actually like it's functions & the power that it has to retain settings, especially since I'm using the Beta IE7, and want my settings "where I can see them".
Good Luck & hope the above workaround works for you.