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.
Updating to the latest ajaxcontrol toolkit should use the same version of the htmlagilitypack.
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.
Updating to the latest ajaxcontrol toolkit should use the same version of the htmlagilitypack.