@ConallofUlster and @FurryNutz,
Saw your posts as I was looking for a solution to the problem myself.
I am running a twonky mediaserver on my dLink DNS-323 NAS - and uses dLinks DIR-825 router.
Some time ago I updated both the twonky software and the router software. Weeks later I streamed a film from the NAS and discovered that my Samsung SMART TV lost connection to the twonky mediaserver every 30 minutes.
Suspecting twonky for causing the problem, I spend some time trying out other twonky software versions - but with no luck. Almost giving up, I started looking into the router firmware version. After some time I DISABLED Multicast Streams in the router - and "voila" it worked Again.
I noticed that other DIR-825 users experincing these kind of problems bump into them after upgrader to firmware versions higher than 2.05 (I upgraded to 2.06 but solved it - hopefully - without having to downgrade but disabling Multicast Streams instead).
Hope this is of use.
BR, Carsten