Bridge Layer lays Bridfge that Tanks cant use

[Boisforas]

Boisforas here with yet another tech problem: In the scenario "Into the Valley of Tears," the Syrian forces include 6 bridge layers(MT-55KS AVLB)which are needed because the map has an anti-tank ditch running N,S top to bottom which the Syrians cannot advance across unless a bridge is laid. So I laid one across the ditch from a bridge layer but the game wont let me move my tanks over the bridge, a box telling me that I cant advance my tanks into that terrain?! What am I doing wrong here? Thanx, Eric