HI,
I encountered the same problem, but found a solution.
Instead of manually deleting the folder of previously installed HDB Clients and Studios as suggested above (I tried that first; it didn't help), I ran hdbuninst - just double-clicked on the EXE in the install folder. This is a command line app, but very simple to use.
I uninstalled every instance that hdbininst reported (5 in my case). You have to run hdbuninst again for each installed copy.
I didn't reboot after any of these uninstalls.
After they were all uninstalled, I reran hdbsetup - just by double-clicking in Explorer.
The moral of the story appears to be: use hdbuninstall, not a manual file delete.