I recently got an iPad 64gb. And have since been loading all of my Comic backups onto it (Via Cloudreaders). I've got 32.5gb used and 26.4gb Free. Every 20-30 issues or so I get an error that says "Comic book name here" cannot be copied because an error occured. There is not enough memory available.
Now the easiest way to fix this is to close iTunes and restart it - This will allow me to add another 20-30 so issues before having to do it again. However that doesn't seem to be right expecially when i'm unable to backup my ipad because I get this error.