[OS X Emacs] Unabel to debug error: "Symbol's function definition is void: screen-width"

[Sriram Karra]

I recently downloaded the latest version from the aquamacs site. There is
some problem in my configuration that is causing the error mentioned in the
subject line when I try to use the mouse scroll button or press C-v.

Even more strangely I am unable to trigger the debugger by setting (setq
debug-on-error t)

The value of debug-ignored-errors is ("^Invalid face:? " beginning-of-line
beginning-of-buffer end-of-line end-of-buffer end-of-file buffer-read-only
file-supersession user-error)

Version: Aquamacs 3.0a GNU Emacs 24.3.50.2 (x86_64-apple-darwin13.0.0, NS
apple-appkit-1265.00) of 2014-01-21 (Aquamacs-3.0a) on watson

I used to use an earlier version of Aquamacs and faced no such issue with
the same config files.

Any clues on how (a) why the debugger is not triggering and (b) what
happened to screen-width variable and who is looking for it?
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