Ubuntu installation not working

[Confused user]

On an Ubuntu 11.04 system, I've been using the D1 version.  Yesterday, I tried
to remove it, and install the D2 version.  When trying to compile "hello
world", I always get

object.d: Error: module object is in file 'object.d' which cannot be read
Specify path to file 'object.d' with -I switch

when I remove D2 and reinstall D1 (always using the one click installer), I
always get this error for both versions.  How do I get back to having a
working installation?