My desktop and laptop computers are both running the same version of Windows 7, the same version of Caibre and the Kobo plugins. I usually use my laptop computer for Calibre and adding and editing epubs to my Kobo Glo. At the moment my sister has borrowed my laptop, so I deceided to add some epubs from my Glo into Calibre on my desktop computer. Opened up Calibre on my desktop computer with Glo connected. Chose the books in Glo and used the "add to library" option and Caibre went through its normal process
Partial success, some epubs transferred over and showed up in library on Calibre others did not. All are epubs with non-DRM. Interesting one that failed to transfer was the epub of Calibre Quick Start Guide

They all showed up in the Calibre library, but with blank covers, titles containing what appears to be random letters and/or numbers and a file size showing as <0.1.
I have tried deleting Calibre and the Kobo plugins and re-installing and trying the process again. Same result.
Anyone have any ideas as to why the failure? Look forward to reading replies and thanks in advance.