[plt-scheme] Unable to get determine shell-mode symbol names

The example in section 15.3 of the mzscheme manual, (shell-execute #f 
"http://www.plt-scheme.org" "" (current-directory) 'sw_shownormal) gives 
me the following error (in DrScheme 'Pretty Big' and in mzscheme started 
from the commandline):

shell-execute: expects type <show-mode symbol> as 5th argument, given: 
sw_shownormal; other arguments were: #f "http://www.plt-scheme.org" "" 
#<path:C:\Program Files\PLT>

I've tried various of the other given symbols (sw_maximze, etc.) and all 
give the same result.

Is this my problem or mzscheme's problem?  If mine, I'd appreciate 
knowing what I'm doing wrong.

Thanks,

Scott