Have you tried doing a complete uninstall (from registry) and re-installing ADI?

To do a complete uninstall:

1. Reboot the PC
2. Close ALL programs that start on startup
3. Uninstall Excel- not necessary unless Excel problems are prevalent
4. Uninstall ADI (with Oracle Installer)
5. Manually remove:
(if on Windows 95/98) :/ORAWIN95/GLDI90
(if on Windows NT/2000) :/ORANT/GLDI90
6. Restart the PC
7. Close ALL programs that start on startup
Before performing this step make sure that all the information from the Define Database window has been written down: FNDNAM, GWYUID etc, since the registry keys are being eliminated these will have to redefined later.

8. To manually delete ADI and GLDI registry entries:
9. Run Regedit.exe
10. Go to HKEY_CURRENT_USER /Software/ORACLE: from here delete ADI and GLDI folders
11. Go to HKEY_LOCAL_MACHINE/Software/ORACLE: and again delete ADI and GLDI folders
12. Restart the PC
13. Close ALL programs that start on startup
14. Reinstall Excel (make sure you also install the Data Access option)
-Data Access not Required in ADI 5.0 or later
15. Reinstall ADI (using the Oracle Installer)
16. If needed apply any needed ADI patches.
17. Restart the PC
18. Close ALL programs that start on startup
19. Try ADI again