Random error - unable to update channel, try again later

Hi, i have a little question.

When i lunch webgrab sometimes, without changing anything in WebGrab++.config.xml, don't update some channels and give me the error "unable to update channel, try again later".

If i lunch again webgrab for example after 20-30 minutes the same channels are update.

What's the problem? i don't change WebGrab++.config.xml

The problems are the server used for take the epg (for example guidatv.sky.it)

Thanks for the support