Running version 8.0.1.1501. We are using ldap.ora; I can tell that my oracle client configuration is good because I can use tnsping to successfully connect to the database. The only variable, really, is that I recently switched to a new machine with Windows 7. When I try to log in to the database, I immediately get an error popup (red X with "OK" button) but no text -- totally blank. And I'm not logged in. Can't log in after that, either. I've put my oracle_home in explicitly, too. Not sure what's happening, any thoughts? Thanks!

Hi m4a1.
Not sure if this is a PL/SQL Developer or Windows 7 problem/bug, but is something I have come across and I believe is undependent of the specific PL/SQL Developer version/build - was using v7.1.5.1398 build.

To make your developer working go through following steps:
1. Open control panel
2. Open "User Accounts" element
3. Open "Change User Account Control Settings" element
4. In the opened window put the slider to the lowest position : "Never notify me when:"
If you can't modify the setting, you will have to contact your administrator to do it.

!!! Keep in mind in order for changes to take effect you will have to retart Windows (the machine).

The above steps worked for me and now I am able to log in the database(s).

Brilliant!! Absolutely right. I should have thought of this... I was never a Vista user, so going from XP to 7, I encountered plenty of issues where apps would behave weirdly because they were not explicitly started in administrator mode. I guess the app would have to have built in hooks to the OS in order to prompt at runtime. The blank error really threw me in this case. Thanks so much for your suggestion!