Update: Brian I know now what is causing this problem when exporting from Outliner for iPad. I exported another Outliner document and it worked fine, and then played around it and I know the cause:

As I am Finnish, there is a letter Ä "A with the dots" and if the filename consists this letter (the same is also probably with "O with the dots") I will get the error mentioned above. So I guess it is a bug related to these scandinavian letters.

Now if I would only be able to remove the unnecessary folders from my OmniSync server folder somehow..