Stalingrad Gold Don Bridges

[Gordons HQ]

At present I am in a PBEM game, Stalingrad Gold, scenario #0723_01 Don Bend as the Russians.
I have a engineer unit at hex location 109 12 adjacent to a bridge over the Don.
I wanted to blow this bridge but when I commanded the unit to do this it does not allow it, it  states there is no bridge adjacent to this hex.
I can't understand this, because on the map the bridge is obvious and when you click on that hex it states it is a bridge hex.
I checked out the other Don bridges and they are all the same when you click on the hex adjacent to them they just state primary road.

Any ideas, this has completely ruined my strategy however improbable that may have been.

Cheers,

Gordon