“Book too large!” is an error message that appears when attempting to use .dupe on a Paper server.

This error message appears because the glitch behind .dupe cannot be used on Paper servers. .dupe must be used on non-Paper servers only.

.dupe is permanently patched on Paper servers. The only fix is to use .dupe on a server that doesn't run Paper.

1. Press F3 to open the debug screen.
2. Check the type of server in the top left corner.
3. Realize you are connected to a “Paper” server, which will never support .dupe.
4. Leave the server.
5. Connect to a different server that is compatible with .dupe.
6. Duplicate items without any problems.

Pressing F3 shows the type of server in the top-left corner.