[plt-scheme] Installation Error with leftparen.plt

Hi,

I try to install leftparen from the repository at planet.plt-scheme.org 
on Mac OS X. Here is the link: 
http://planet.plt-scheme.org/display.ss?package=leftparen.plt&owner=vegashacker

According to the instructions, I run in DrScheme:

 > (require (planet "leftparen.scm" ("vegashacker" "leftparen.plt" 1 2)))

and get the error:

standard-module-name-resolver: collection not found: "scheme/base" in 
any of: (#<path:/Users/eckhard/Library/PLT Scheme/372/collects> 
#<path:/Applications/PLT Scheme v372/collects>)
 >

What does that mean and how can it be fixed?


Thanks in advance

-- 
Eckhard