[georgemk]

@quoddle

Looking on the internet for that error message, it seems that this error occurs where you have 2 or more programs each with their own version of the QT software (which Calibre uses too) and the interactions between them. Basically 1 program finds the wrong QT files at runtime (an incompatible version) and the result is this message.

Have a look in your "System Environment Variables" for any variable name starting with QT and if found see what software uses it. That is one possible cause as it would divert Calibre from loading its QT files and try to load another program's version.

Don't just delete any such variable you find but investigate as you could stop something else working - you'd be surprised at how many programs use QT behind the scenes.