I also have the latest firmware update.

Missing from your post is any specific details.
1) We need the name of the file. The full name of the file would tell us not only the kind of library (acoustic guitar which is of minimum importance) but very importantly the .n1.x3a, or .n2.x3a, or .n3.x3a suffix would tell us exactly where the manufacturer of the Library installed the Waveform List and Samples. The n1, n2, n3 designation gives us a clue where the new data is housed within the file.
This is critical in avoiding the message you are receiving. The ".n1" means FL2 (nothing for FL1); the ".n2" means FL1 (nothing for FL2); the ".n3" means USR (nothing for either FL1 or FL2)

2) in place of the above, the installation instructions that typically accompany a library file would surely indicate in which of the 512 + 32 (Normal + Drum) Voices being loaded the new Waveforms are used... typically they additionally indicate which Voice Banks are used for the new Voices. Again critical info when attempting to redirect the Waveform List and Samples to the FL2 slot and your internal memory.

3) the exact Load Option setup you tried that gives you the error message. Usually a specific error message is chosen from a list of error messages in response to the specific error encountered. It is telling you that your data is being directed to an empty or unformatted slot. Presumably, that is FL1 since you have formatted (and hopefully verified) FL2 is presumably waiting for data. So the message might be accurate, are your directing the data to FL2?

The Load Option appear in the lower right area of the File screen... here's an example Load configuration that would likely work... (guess)

USR > FL2
FL1 > FL2
FL2 > None

The above setting is taking whatever is in the File and targeting FL2. And should be the Load Option setting if the file has the following extensions

*.n2.x3a or *.n3.x3a

It literally translates to:
If the new Waveforms are saved in the User Sdram take them and install them in FL2 (USR > FL2)
If the new Waveforms are saved in FL1 take them and install them to FL2 (FL1 > FL2)
If the new Waveform are saved in FL2 .... that would be news as most commercial libraries hardly fill slot 1... highly unlikely the original author stored the data in a commercial library in slot 2 ... no one would assume 2 Flash Boards.

Direct the stored data > to a target Flash Board.

It's done! I replaced the flash to slot 1, reformatted and Hey Presto!! Happy days..