Unexpected character encountered while parsing value

Possibly you are not passing JSON to DeserializeObject.

It looks like from File.WriteAllText(tmpfile,... that type of tmpfile is string that contain path to a file. JsonConvert.DeserializeObject takes JSON value, not file path - so it fails trying to convert something like @"c:\temp\fooo" - which is clearly not JSON.

I solved the problem with these online tools:

1. To check if the Json structure is OKAY: http://jsonlint.com/
2. To generate my Object class from my Json structure: https://www.jsonutils.com/

The simple code:

RootObject rootObj= JsonConvert.DeserializeObject<RootObject>(File.ReadAllText(pathFile));

In my case, the file containing JSON string had BOM. Once I removed BOM the problem was solved.