Enrico, there is no size limit for Aperture libraries.
If the copying did not succeed, there may be a problem with the contents of your library (a file with an incompatible filename, for example.) You'd better try to find out why, before you split your your libraries, for splitting may not solve the problem.
but it din't finish the work for a error.
What is the error message exactly?
How are you copying? Are your drives directly connected, or are you using a network to copy?
Are both drives formatted MacOS X Extended (Journaled)? If your destination volume still has the default formatting MS-DOS (FAT), there may be ambigious filenames and copy conflicts.
Can you see, what the last file that has been copied has been? Is there a partially copied library on the destination volume? Then inspect the image that should have been copied next, and look at the filename and if it can be opened.
Regards
Léonie