To resolve, you need to configure IIS logging manually.
1. Run the Internet Information Services (IIS) Manager snap-in on the Exchange server from which you want to gather OWA activity statistics.
2. In the treeview, browse to the Web sites node.
3. Right-click the web site that you want and select Properties.
4. On the Web Site property sheet, click Properties in the logging section.
5. In the Logging Properties dialog, review the settings on the General property sheet.
6. Select the Advanced tab.
7. Select the check boxes next to the following extended properties:
Date
Time
Client IP Address ( c-ip )
User Name ( cs-username )
Method ( cs-method )
URI Stem ( cs-uri-stem )
URI Query (cs-uri-query)
Protocol Status ( sc-status )
Win32 Status ( sc-win32-status )
User Agent ( cs(User-Agent) )
Cookie ( cs(Cookie) )
8. Click OK to close each window and apply the settings.
After that change, all new gatherings should be successful.