Thanks for using Aspose APIs.
We were able to observe this issue and logged it in our database for investigation and for a fix. Once, the issue is resolved or we have some other news for you, we will let you know asap.
This issue has been logged as
CELLSNET-45837 - Spreadsheet XML gets invalidated because it contains elements with double prefix e.g. <o:meta:generator> etc.
Workbook wb = new Workbook("SAU Rapporter.ods");
We found the following line invalidates the XML.
<o:meta:generator>NeoOffice/3.0.2$Unix OpenOffice.org_project/Patch 0</o:meta:generator>