If you press the plate combinations 1-3 or 1-4, does the smoke turn red again, like it does when you press 1-2?
Can you jump around the gate, or is that blocked?
It is a little tricky, but I jumped up and out, then back in to get to the second level of some scaffolding (which was very annoying since for the timing and effort required there was nothing on the body there). It might be possible to jump up and to the right past the gate, and get back left enough to land on the ledge; then again, that may have been deliberately blocked so people would have to figure out the statues.
You might want to try doing a clean install of the game. That may help if the problem is in the game itself, rather than the save.
If that doesn't work, you could try emailing the save to Larian (support@larian.com) and see if they can open the gate.
In XP the saves are in the folder
C:\Documents and Settings\ %username% \Local Settings\Application Data\Divinity 2\Savegames
or in Vista / Win 7
C:\Users\ %username% \AppData\Local\Divinity 2\Savegames
You may need to set Windows Explorer to show hidden files and folders.