Hi Blackbird!
You are experiencing the same thing that everyone experiences here. The advice from Bert is good... save your game just before drawing the snake because it's a long walk back otherwise.
Anyway, I have written about this before and I'll paste the advice here:
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Nobolen - Island Door won't open
We have had a number of folks who got stuck here.
Here's what I can tell you about the most common problems...
1. After dropping the slate, link back to the bubble where you first arrived (there is a symbol on the pedestal for returning to the starting "bubble"), then run to the island from there. Some don't link to the bubble... they climb back down all the way and can't get to the island in time.
2. Some don't know about the RUN control. When you link to the bubble, you have to turn and RUN all the way to the island door. RUN is done by holding down the SHIFT key as you click forward with the mouse. You go much faster, which is needed!
3. Some get to the island door by running, and aren't patient enough to allow enough time for the door to open. By running, you get there about a minute before the door opens...so wait it out (longer than a minute to be sure).
4. This is most common, and we've discussed it before.... the dreaded "The Bahro didn't recognize the drawing" problem. The way to find out of he recognized the drawing is to look on the Lower Left of the slate to see if the Slate has a shortcut for the snake (after the "run"). If it doesn't have the snake shortcut, he didn't recognize the symbol... so you'll have to try again (...and again, and again till you get it right). The problem here is that it takes a long time to reload the save and try again, but "them's the facts".
"Persistence is a virtue" ---------------------------------------
ALSO, saves cannot be shared for this game... the save structure is too complex, so it is up to you to get this one.
Hope this helps!
Dadguy