[narada]

Thanks for the reply.
But I couldn't find it out. So I deleted the files one by one...
The dot appears first like ".Prelude" and refers to "Prelude" in the same folder.
I think it's a file that apple creates, and is invisible on my macbook, and so I 'group-imported' along with the correct files.
If I open de ".Prelude", MobileSheets crashes.
Last week I bought the app, and yesterday I bought MobileSheetsPro, so I don't know if the Pro version would crash also.
Importing my whole library to the Pro version was easy and flawless.