Hi,
You probably need to give the poller-wrapper more threads to complete polling in ~5 minutes.
It's possible that your system isn't fast enough to complete polling in that time, but if you have lots of devices which are slow to respond, increasing threads will help.
You do this by increasing the number of poller wrapper threads in the web config interface.
Don't increase it too much, otherwise you'll cause other problems.
You can see how long the poller wrapper currently takes by looking at the /pollerlog/ page.
Adam.