I can see impdb.exe in E:\Oracle\product\11.2.0\dbhome_1\bin, and that folder is in the PATH. But when I open a CMD window and try to run impdb, I get the error in the title. I can verify the PATH is correct, because I can run the imp command from the same folder. Using the full path name to impdb does not help. I can run impdb by double clicking it in Windows Explorer, but that does not let me specify the command line args I need. I have checked both imp and impdb with Dependency Walker, and they are both missing the same demand loaded DLLs. This is a Windows Server 2003 x64 machine, if that makes any difference.
