Either your opkg-list got corrupted somehow or there is some checksum mismatch. Try removing /tmp/opkg-lists and then rerun 'opkg update' and try to install again 'opkg install nodogsplash'. If this doesn't work, then try install them manually by downloading them from the repository.
http://downloads.openwrt.org/barrier_br … ages/base/
Download the following packages:
iptables-mod-ipopt_1.4.21-1_x86.ipk
kmod-ipt-ipopt_3.10.49-1_x86.ipk
libpthread_0.9.33.2-1_x86.ipk
Then try to install them by 'opkg install [package.ipk]'. If that doesn't work also, then you can unpack them in the /tmp/someSubDir dir by 'tar -xzvf package.ipk' and install the contents of the data archive manually. This a last resort so use only if everything else failed.
Before all, you should check if the packages aren't already installed. Run "opkg list-installed | grep [part of the package name]". Look directly for the modules by 'ls /lib/modules/`uname -r`/xt*' or 'modinfo xt_ecn.ko'.