I suspect it could be a WiFi coverage issue. Tried putting the wireless router right next to the PS3? And while you're at it try a wired connection to rule the wireless out.
I get the occasional DLNA error. Generally it's when WiFi around the house is playing up and my laptop also loses signal a bit.
But generally it works fine even though the DNS isn't (apparently) officially DLNA certified. I didn't do anything special - just enabled the media server in the DNS, searched for media servers on PS3 and it just started working.
The only issue I have is that the PS3 doesn't refresh the content on the DNS. I've read numerous threads with the same issue saying to for a refresh within the DNS, and also to do the refresh with the PS3 off but it doesn't do any good. Sometimes it will update but for no apparent reason.