I had attempted a move earlier in a game I am playing that failed, and I'm not sure why. Here's the move:
A Bre -> F English Channel via convoy
F EC -> convoy from Bre to North Sea
F North Sea -> convoy from EC to Denmark
F Heligoland Blight -> Support move to Denmark from North Sea
There was an enemy army in Denmark, Norway, and in that same turn I was able to dislodge the enemy in Kiel (so Kiel would not have been able to support Denmark). There were no other units close to Denmark, unless you count Berlin, but they don't connect and Berlin wouldn't be able to support Denmark
At the turn, I was told the support move was not accepted and the army was unable to move into Denmark. It doesn't matter now in that game, since I just used my fleet in Heligoland Blight to take it the next turn. But now I'm stuck with an army in the wings that I could have easily used in Germany supporting or advancing.
But it does matter again, since I am faced with a similar situation. The army that was in Brest is now in Belgium, waiting to be convoyed to Norway through the North Sea with support from Norwegian Sea, Denmark and Sweden. But if the move is not possible, I want to do something else. The game is 2189 if it matters.