Issues with co-authoring Documents in SharePoint 2010

If you cannot co-author a Word document or PowerPoint presentation, then one or more of the following reasons may be the cause:

• The file is using Information Rights Management (IRM) or Digital Rights Management (DRM).
• The file is checked out.
• The file is encrypted.
• The file format is not supported. Only .docx and .pptx file formats are supported. In most cases, you can save the unsupported file format in the supported format.
• The file is marked as final. The file owner has decided to stop the process of editing or co-authoring the file and the file is now read-only.
• Certain Microsoft Office group policy settings prevent co-authoring including the following: Disable Auto merge Client Policy, Disable Co-Authoring Server Policy, and Disable Co-Authoring Client Policy.
• The file contains an ActiveX controls.
• The file contains certain objects that cannot be uniquely identified, such as an OLE object, a SmartArt graphic, chart, or Ink object.
• The Word document uses master documents with subdocuments, contains HTML Framesets, or is being published as a blog.
• The Word document does not have the Store random numbers to improve Combine accuracy check box selected. (On the ribbon, click the the File tab, click Options to display the Word Options dialog box, click Trust Center, click Trust Center Settings to display the Trust Center dialog box, click Privacy Options, and then under the Document-specific settings section, make sure the Store random numbers to improve Combine accuracy check box is selected.)