The error you describe might mean that UniDAC didn't find the specified "Client Library" or that the client library doesn't match the bitness of your app.
Please be informed that UniDAC interacts with server through client library with help of special API.
Client libraries are not included in UniDAC, since the UniDAC can access different versions of both InterBase and FireBird.
The FireBird client library is distributed with FireBirde.
Moreover, the bitness of the library should correspond to the bitness of the application.
You need to deploy the FireBird client library file and set the path to it in the TUniConnection.SpecificOptions.Values['ClientLibrary'] property."
Please check that you have the required client library to operate with the FireBird server you are using.
Kindly note that the question about how to receive client library is not related to functionality UniDAC.
However, as an option, you can download the FireBird server as an archive from the official FireBird website and then take the required library from there, also feel free to contact FireBird technical support to find out where to download and how to install the FireBird client.