The win32 installer is not including or deleting the pg_tblspc directory and this is causing problems to PGSQL admin programs that us the pg_database_size function.
Here is a screenshot verifying the directory is missing from a fresh install of Postbooks on windows:
The postgresql server needs this directory and it should be there as it's created during the initdb phase of the standard server install.
Thanks for the heads up! I passed the information to the Windows installer developer, and he tells me the fix is in for the 2.3.2 release.