[plt-scheme] Internal PLaneT error: trying to install already-installed package

I'm trying to use the new DrScheme 4.0 installing the pgsql schematics
Planet package

(require (planet "spgsql.ss" ("schematics" "spgsql.plt" 2 3)))

gives me the following error:

Internal PLaneT error: trying to install already-installed package

and will not run any code after that.

I was curious if anyone else has encountered this error?

I tried it both on Windows XP and Mac OS X 10.5.2.   If I comment out
the check that throws the error in "collects/planet/resolver.ss" it
just returns a void package - even though I can see all the files
there in ~/PLT Scheme/planet/300/packages and ~/PLT Scheme/planet/
300/4.0/cache.

Does anybody have any ideas why this would be happening?