Oh, I see the problem. You might want to reread the scripting post on this, as I explained this to another fellow.
viewtopic.php?t=12073
I'll reiterate here. This tool works just like the LM create shape tool generally. You may want to review the manual on that.
http://www.lostmarble.com/moho/manual/fill_tools.html
Look for 'Create Shape'.
Try this:
1) create a circle without any fill or outline, with the oval tool
2) using syn_create_shape tool, select what kind of shapes you want to create (both, outline only, fill only) in the tool options at the top of the workspace
3) with this tool, define a shape to be filled
4) hit the space bar to finalize the shape
If you are using a tool that does auto-outlining/filling (like the oval, rectangle, or freehand tools), then you have already created the shape and can only change it by selecting it with the select shape tool.
Like the LM tool, this only works for the initial creation of shapes. (Shapes are the fill/outline you create to make vector curves visible when rendered.)
The tool is only clickable after you have some vector curves to creat shapes with.