That is not a WRT610N specific problem, you just fell into the trap of installing a trunk snapshot one day - and then trying to install further kernel modules several days later (which were built against a different/ newer trunk snapshot).
Trunk snapshots are rebuilt roughly daily, but kernel modules (and their corresponding module packages) need to match exactly to the kernel they've been built against. In practice this means you can only install (module-)packages built in the same build run as the firmware you installed, so basically from the same day as the trunk snapshot you downloaded and flashed. This means you either need to install all potentially needed packages right away after flashing your trunk snapshot or mirror all packages corresponding to the firmware you're going to flash (and then feed those to opkg instead of the fresh ones on download.openwrt.org).
Unless you have special reasons to use a trunk snapshot, it's probably easier for you to just flash an official release firmware - whose /etc/opkg.conf points to a (mostly-) frozen package tree corresponding to the release firmware you installed, so you can 'always' install matching packages later on.
(Last edited by slh on 20 Jan 2015, 00:21)