sfp trunking

Hello

I am new to managed switches and I would like some help with configuring two Netgear switches (GS716Tv3 and GS110TP). I am trying to configure a trunk link between these switches using two SFP modules on each switch. My goal is to configure a trunk that will allow as much traffic as possible, since there are 'heavy' users on either end of both switches.

I read the document http://www.downloads.netgear.com/files/GDC/GSM7352SV2/how_to_configure_lag.pdf and that seems pretty straightforward, but apparently I am missing something. Connecting the switches using one SFP port on each switch seems to work fine, but as soon as I connect the second SFP port on each switch with a glass fibre cable, both switches seem to enter in a loop or something. 

I assigned ports g17 and g18 of the GS716Tv3 as 'trunk member' to LAG ch1, and ports g9 and g10 of the GS110TP as 'port channel' to LAG1.

What am I missing here? Can you please point out how I have to configure my switches? And secondly, am I right in assuming that a double SFP link allows more traffic than a single link?

I hope that my description above makes sense, since english is not my native language.

Thank you in advance,

cabwav