ÝTT enter clearance to Croatia
 

Anybody could give more light.
Today at about 1200 1300 UTC
over Austria an ÝTT? flight at FL400 just could not get Zagreb ATC to approve their FPL. They very politely tried everything
but the very terse answer was also very brief
'Go back to your previous frequency, or come back with a NEW FPL'
All we could hear afterwards was that same flight was holding at FL400 at Cro Border entry WPT