I believe your file structure is not correct.
Did you create a virtual directory for testing?
Let's do a test:
Copy the CuteSoft.Chat. dll, CuteSoft.ChatService.dll, sampleportal.dll to your bin folder in your web root.
Your error message should disappear.
asp.net Chat http://cutesoft.net/ASP.NET+Chat/default.aspx
Web Messenger: http://cutesoft.net/Web-Messenger/default.aspx
asp.net wysiwyg editor: http://cutesoft.net/ASP.NET+WYSIWYG+Editor/default.aspx
asp wysiwyg html editor: http://cutesoft.net/ASP
asp.net Image Gallery: http://cutesoft.net/ASP.NET+Image+Gallery/default.aspx
Live Support: http://cutesoft.net/live-support/default.aspx