You get a message that says the radio message cannot be found right? It comes up at the middle of the screen? If yes then I had the same thing at the start. I'll tell ya what ya need to do.
This was in one of the example missions wich came with Toadlife's tutorial:
Just look at the things I have in my stringtable and description files. And then modify them at your will.
Stringtable.csvLANGUAGE,English,
STR_CFG_PAPABEAR,"King Six",
STRM_KINGSIX,"All units report in.",
I noticed that you only need to configure one STRM. After that you just make him talk with the name you defined in the init.sqsDescription.ext class CfgRadio
   {
   sounds[] = {kingsix};
      class kingsix
         {
         name = "kingsix";
         sound[] = {"kingsix.ogg", db+0, 1.0};
         title = $STRM_KINGSIX;
         };
   };
You need to configure the radio untill you can get the command to work. Then just make King Six, in your mission whatever you choose ,talk the one STRM and after that you just make him talks normaly. He actually talked with sidechat after I had once used the sideradio command. I hope this helped you out. If you want to use something other than King Six (I think you do ;D ) then just replace all the King Six related things with your own. But use Caps Lock and write the words in a row like I did there but just replace the name. You know what I mean.
I hope this helped you out!
Hawki