The background to this query was this question.
I have installed this driver for Firebird and placed it within the path (system32) used by the IDE. The XE Data Explorer
The basic question I had (in part I) was:
I want to install a Firebird database driver, and to have it available within the Delphi XE IDE. I want the database driver to be usable on the same basis as other, supplied database drivers (eg Interbase, SQL - from within the Data Explorer in the IDE). I have obtained an appropriate driver.
After considerable investigation I have found that it is not possible to achieve the integration into the Delphi IDE that I was trying to achieve. This is because the Data Explorer is a .NET application and the available DBExpress drivers (here and here) are just not compatible with .NET. I understand that I can use the drivers by setting up the parameters appropriately, in both the IDE and by programming in the application I am developing.
I have drafted this answer to assist others to avoid this particular blind alley. I am also editing the part II question in order to remove a lot of the detail, that proves to be unnecessary in the light of this answer.
The first thing that sticks out to me is that you're using the 64-bit version of Firebird, and that you mentioned it comes with both a 32- and 64-bit driver. Are the DLLs named the same? If so, I suspect that the IDE/OS are trying to load the 64-bit version of the DLL in a 32-bit application, which isn't possible (32-bit apps can't load 64-bit drivers, and vice versa).
Try one of two things:
First, if the DLLs have the same name, rename the 64-bit version temporarily, and restart the IDE. Then try again.
Try installing the 32-bit version of Firebird, even though you're running a 64-bit OS.