Sharepoint - UserAgent not available, file operations may not be optimized

This error has the most simplest answer. I saw that pages in my SharePoint 2007 environment was customized using SharePoint Designer, Once I reset the page to site definition everything started working (without any errors).

I suspect that when the pages are customized in Designer, the HTML scripts for pages are taken as it is through database migrations, and SharePoint 2013 is not smart enough to render the customized pages based on old definition.

Learning, reset Designer customized pages to site definition in case site throws error after migration. This means that you will have to lose all your customization.

Please feel free to post any better answer, in case you find one...

Weird but true...

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