[plt-scheme] draw.ss - (lib "draw-sig.ss" "htdp") appears in red

I was looking at this code in htdp/draw.ss using DrScheme:

1 #cs(module draw mzscheme
2   (require (lib "big-draw.ss" "htdp")
3            (lib "draw-sig.ss" "htdp")
4            (lib "unitsig.ss"))

All of line 3 is in red, but the file exists and the module browser  
sees draw-sig.ss.  I'm using v360 on Mac OS X.  My setup is  
conventional, except for the object-debugger I installed prematurely  
the other day, which requires v369 > v360.  Since that day, I see  
this boot message:

Users/gknauth/Library/PLT Scheme/planet/300/360/cache/plt/object- 
debugger.plt/1/0/tool.ss:15:14: unit: exported variable is not  
defined at: drscheme:tool-exports^ in: (unit (import drscheme:tool^)  
(export drscheme:tool-exports^) (define sequence-trace-language% (c...

Is that why line 3 above was red, or is it something else?

Geoffrey
--
Geoffrey S. Knauth | http://knauth.org/gsk