In the Plug-ins folder I have Ai2CanvasMac.aip at the top level which looks like it's an older plug-in. Within the Plug-ins/Extensions folder I have the following, which I think were installed by Illustrator:
3D.aip
CharParaStyles.aip
IdeaFileFormat.aip
Perspective.aip
SwatchLibs.aip
Action.aip
ColorHarmony.aip
KeyboardShortcuts.aip
PlanetX.aip
SymbolPalette.aip
ActionPalette.aip
ContextMenuTouch.aip
KinsokuDlg.aip
Print.aip
ToolSelector.aip
AppBarControls.aip
ControlPanel.aip
Layers.aip
SVGFilterEffect.aip
Transform.aip
ArtStyle.aip
Deform.aip
LinkPalette.aip
ScriptingSupport.aip
TransformPalett.aip
ArtboardPanel.aip
DocInfo.aip
LiveBlends.aip
ScriptsMenu.aip
TransparencyPalette.aip
AssetMgmt.aip
DynamicCorners.aip
LiveShapes.aip
SeparationPreview.aip
VariablesPalette.aip
BNPlugin.aip
FWAlignADM.aip
Navigator.aip
Services.aip
Vectorize.aip
BeautifulStrokes.aip
FlattenS.aip
Nudge.aip
SmoothShade.aip
Workspaces.aip
BrushManager.aip
FlatteningPreview.aip
Package.aip
Snapomatic.aip
altglyph.aip
CSSExtract.aip
Geometry.aip
PaintStyle.aip
StrokeOffset.aip
fileclipboardpref.aip
Also in the Plug-ins folder are these folders (which I think were installed by Illustrator):
Illustrator Filters, Illustrator Formats, Illustrator UI, Photoshop Filters, Photoshop Formats, Text Filters, Tools.
The only thing that looks a bit odd to me in those folders is "Expert Font Table" (in Text Filters) which has a different icon and is a Unix Executable File.
I'll try removing Ai2CanvasMac.aip, see if that does the trick.
Thanks
Christine