what is the switch? Do you use 802.1Q VLAN?

Have you checked the setting of the other router?

Why not set the modem as bridge mode?

I think the UG of the product have expalain the LACP detailly. You can refer to it for help. Maybe you can export the config file, and reset the switch, and then reconfig the LACP, I believe it is...

You can reset the switch through Hyperterminal, After you accessed the login page, pull off the source supply and replug it, meanwhile press CRTL+B at same time as soon as possible, then you can use...

I think your conig is wrong.In your situation, I think the Port Based VLAN is more suitable for you. You can have a try.