Can't get Radio to play Music
Great work! 
Glad your problem is solved. 
I guess I now just need to work out what entity I need to use to trigger it in the PTI map, at least I understand better where the problem's at now, thanks.
Moral of story: Don't edit PTI maps in Hammer. 
Well unfortunately I don't know Hammer well enough to create my own full maps yet.
Theres many Hammer tutorials on YouTube, I suggest you go watch it. Also, the Portal 2 Mapping Wiki (Seen at the fourth tab on the header, just below the ThinkingWithPortals.com logo) or the Valve Developer Community Wiki has alot of information about the things about both Hammer and PTI. Thats how I learned about Hammer. ^^v
Sure, I acknowledge that. I'd still like to know what's causing the issue if possible though, it helps me learn.
I had exactly the same issue with my contest entry map. I added a radio, and wanted it to play music in a 1024 area at volume 7, but it just refused to work!!?!
I believe the issue is caused by the re-arrangement of files that comes with DLC1 and/or 2
Things that worked properly prior to the release of DLC1, no longer work properly
for example, if I create an ambient_generic and then search for 'Raw' sounds with the filter of 'Glados', the ONLY sounds I can hear are ones from DLC1
This problem is surely related to one or the other of DLCs
"Such monstrous sucking-constructions aren't built within one afternoon"
[Released] Power Interference
[Released] Rust and Dust (Spotlight Map!)
[Released] Multiportal
I believe the issue is caused by the re-arrangement of files that comes with DLC1 and/or 2
Things that worked properly prior to the release of DLC1, no longer work properly
for example, if I create an ambient_generic and then search for 'Raw' sounds with the filter of 'Glados', the ONLY sounds I can hear are ones from DLC1
This problem is surely related to one or the other of DLCs
Entirely possible, the DLC broke a lot of stuff