When creating the project, by choosing the "image" mode as the destination, you can be confronted with this message if your device containing the image is of the same capacity as the processed device.
A 500 GB disk cannot be contained on a 500 GB disk (Only in image destination mode).
The reason is simple, after formatting your destination, the capacity of your device will be lower than that announced by the manufacturer.
A 500 GB NTFS formatted device will offer you about 465 GB of available space, so there will be insufficient storage space to hold the 500 GB image plus project information.
The solution is to take at least one larger disk, or even a very large disk (3TB), so you can group several clients on a single disk.