Interesting, it tries to save the .apnx, but can't because the .sdr/ folder doesn't exist.
That is a rather long pathname though. Perhaps Windows simply cannot find the folder.

Try making the title shorter in calibre -- Many people use a second column for subtitles. Additionally, you can use the template
Code:
{author_sort:list_item(0,&)}/{title} - {authors:list_item(0,&)}
to only use the first author.