Serious Sam 2 Help

[ACPCUP]

I am playing Serious Sam 2 and i am stuck!! I am in Level:

Foresaken Compound and by RIG 13

I have killed all the A1's but i am by the gate which is locked!! How do i get throught the gate? I have gone backwards looking to see if i missed anything, but there is nothing about! This is the area where there were a line of 'Tank guys' on the rigging above and loads of guys running towards you. They have all been eliminated.

Help!!

 

[ACPCUP]

Can't see any switches etc. No enemies as far as i can see, looked everywhere!! Can't take a screen shot now as i am in work!

 

[ACPCUP]

I seem to recall there is a bug in that level - some of the bad guys don't spawn, and then because you haven't killed everything the gates don't open. I got stuck at the same place and had to start the level over again....

Yea, just found that out on another site!! At what point does the level start?
Thanks mate.