There is an issue with a media node if the media node's name is empty. It is not possible to create a media item without name using backoffice. However it is possible using an API. I had that issues when my custom media import scripts somehow created an empty media node.

Its the issue discussed here http://issues.umbraco.org/issue/U4-5890

the errors : The valueDictionary is not formatted correctly and is missing any of the 'nodeName,__nodeName' elements.

Affected version: 7.1.6 and above.

How to reproduce: 1) first create a media with a empty name.

 var mediaService = ApplicationContext.Current.Services.MediaService;
    var create = mediaService.CreateMedia("", 2000 , "Image");
    mediaService.Save(create);

2) try to read the media later on

var m = Umbraco.TypedMedia(idOfEmptyMediaNodeName);

It throws the error "the valueDictionary is not formatted correctly and is missing any of the 'nodeName,__nodeName' elements"