This usually happen when your system is blocking access.
Quote:
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E:\Programs\Calibre\Calibre Library is not valid:
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You really should not copy a library into Windows PROGRAM directory. User data should copy in a user directory.
If you want make a manual copy, copy the complete directory including all sub directories and files in your user directory (this is something like c:\users\YOUR_USERNAME\... at your new PC. Take care to copy your calibre preference directory too to the correct place (usually c:\Users\YOUR_USERNAME\AppData\Roaming\calibre\
You will find all information's regarding backup in calibre's manual:
https://manual.calibre-ebook.com/faq...backup-calibre
Edit: had't update the window and not seen Kovid already gave you a answer