I have changed the SP 2010 Site to 2013 UI mode. In the Master page gallery, I can see the custom MasterPage. I tried to edit the properties of the master page. In the "compatible UI version", I unchecked the "4" and checked
the "15". I clicked on save. I am getting the error as "The server was unable to save the form at this time. Please try again."
According to your description, there were an error when you changed the UI version in SharePoint 2013.
Was the user that you used a farm administrator?
Did you install other components for IE or SharePoint?
There are some aspects which may cause the error. For resolving your issue, you are able to do as the followings:
1.Give the user Full Control
2.In CA, restart Search Host Controller Service at Manage services in server
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