Well, this is strange. It appears that for somewhere around the 990th book, calibre is sending information that CC thinks is illegal. The log doesn't have enough information to tell me what information is causing the problem or which program (CC or calibre) is broken. If you look at the books around that point, is there anything unusual about the metadata? A wonky date? Odd characters in the title or authors names? A bizarre series name or identifier? Do any metadata fields contain single or double quotes?
One thing to try: in calibre sort by title, then move the 960th through the 1000th book to a temporary library. Does the problem go away? If so, then move the books back bit by bit until the problem returns, at which point you will know which book is problematic. Sam could undoubtedly use the metadata from the book to figure out why calibre and CC disagree.
Another thing we can try if you are willing. If you email me the metadata.db file from the offending library then I can try to repeat the problem with calibre in debug mode. I don't know if I can repeat it. Also, if you send me the db I will know what is in your library, which is could easily be a privacy concern on your part. If you are willing, zip it then email it to the same address. Or put it in the cloud somewhere and email me the link.
For completeness:
- Have you totally shut down and restarted calibre? I mean completely shut it down, not leaving the server running in the task bar.
- Is the content server using a search expression or a virtual library for that library?