Newtonsoft.Json error after upgrade to 3.8

Hello,
after upgrade of web site to version 3.8 I receive follow error (always the same); strange issue is that disappear after update of global.asax (to force the compilation) but after navigation it appears again.. really strange. For my point of view we have issue of authorization (I copied the right test site from test server to production). Any idea? Thanks in advance
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Could not load file or assembly 'Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Assembly Load Trace: The following information can be helpful to determine why the assembly 'Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' could not be loaded.

WRN: Assembly binding logging is turned OFF.
To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1.
Note: There is some performance penalty associated with assembly bind failure logging.
To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog].

Are you using any third-party plugins? Please ensure that you have only one "Newtonsoft.Json.dll" file in your solution. It should be in the \bin directory. It should not be duplicated in one of directories in the \Plugins one

Yes, I am using SevensSpikes plugin. Anyway I will check if Newtonsoft is unique and inform you. Thanks

Make sure your web.config got updated properly.  I was having this issue and my config had the old binding redirects in it.

Thanks. I will check.. but bad issue is the original Nop 3.8 source file with my database produce same error. I suppose that it is related to some Plugin into database. The only own data is the database ..