I am working with the source code version. Here is solution I came up with and it worked for me:
An older version of HtmlAgilityPack was referenced from the BugNET_WAP project and 'Copy Local' was set true for this project.
the location of the dll was this: \BugNET-1.3.242-Source\src\packages\AjaxControlToolkit.4.1.60919\lib\40\SanitizerProviders\HtmlAgilityPack.dll
which seemed not to be the correct one.
However the BugNET.MailboxReader project was referencing another version of the HtmlAgilityPack which was not being copied to the bin folder.
I just removed the old reference from the BugNET_WAP project and added a reference to the dll located at \BugNET-1.3.242-Source\src\packages\HtmlAgilityPack.1.4.6\lib\Net40
That fixed the assembly loading error.
An older version of HtmlAgilityPack was referenced from the BugNET_WAP project and 'Copy Local' was set true for this project.
the location of the dll was this: \BugNET-1.3.242-Source\src\packages\AjaxControlToolkit.4.1.60919\lib\40\SanitizerProviders\HtmlAgilityPack.dll
which seemed not to be the correct one.
However the BugNET.MailboxReader project was referencing another version of the HtmlAgilityPack which was not being copied to the bin folder.
I just removed the old reference from the BugNET_WAP project and added a reference to the dll located at \BugNET-1.3.242-Source\src\packages\HtmlAgilityPack.1.4.6\lib\Net40
That fixed the assembly loading error.