Got help from ED support - managed to resolve issue by:
1. disable McAfee Realtime Scan.
2. add the 2 .dll files from Mod/aircraft/F15E/bin to the virus scan exception files.
3. from DCS/bin directory run the "DCS_update.exe cleanup" command
4. from DCS/bin directory run the "DCS_update.exe repair" command, selecting Slow option and extra files.
Hope that works for you.
An odd process if engine needs to be running to get radio to work? That is ... start engine, then use radio to call tower for permission to commence start up? Minor detail overall - not a big impact to game play overall, just a bit odd.