Microsoft Office Word/Excel documents fails to open with ‘Document Information Panel was unable to load. The document will continue to open. For more information, contact your system administrator message.
After some digging, it looks like the behavior is visible only when you have Managed Metadata columns in the library. But surprisingly it has nothing to do with Managed Metadata service or term store.
Likely cause of this issue was having multiple version of Office products installed in your computer. I have Microsoft Office Professional 2010, SharePoint Designer 2010 and SharePoint Designer 2013. Also have Project Professional 2013. Because of these different version Office products, it messed up some default parameters. Not sure about any of those in detail. But what worked for me was a ‘Repair to Office 2010 suite in my machine’ as suggested in many other blogs.
Go to Control Panel -> Programs and Features -> Select Microsoft Office -> Select Change. Let it load for a minute.
Issue is solved for me after the restart.