First, suggest posting your own and not changing subject line ... original posting issue is similar but for version 2.5. 2.5 is not 2.6. There could be many factors as to why 1.9 -> 2.6 is not working for you. Maybe the moderator can do this for you.
Welcome to the new .... and now some questions concerning your backups ... your 1.9 was what version of 1.9 - can be seen in the moodle.xml file of the unzipping of the backup zip file - the .xml file is text so open with NotePad or some text editor. That will also show all files contained in the course - course_files folder.
If one cannot restore the .zip backup, then at least one still has the files associated with that course in course_files.
One can get an idea of what was contained in the 1.9 backup also by looking at moodle.xml (activities/blocks). If there was an add-on mod or block in the 1.9 that doesn't exist in the 2.6 that could cause issues.
Check the moodledata folder for your 2.6 and look in temp/backup folder to see if there is a folder name that looks like: f7f5f22a0ce99641ec5ed0e38976fa9a
The extracted files are in there. Also see if there is a .log file larger than 0 bytes. That's a text file and might contain clues.
Some 1.9 backups do take some work to get them restored into 2.x. So investigation is required. Have to warn, that even after that, one might have to be happy with just being able to recover the files from the backup - ie, the course will have to be re-built.
'spirit of sharing', Ken
