If you do have Anti-Virus or Indexing service running in the background, you may try excluding the "Temporary ASP.NET Files" folder from the service and see if it works.
If you still have problems, please check the following link:
#Diagnose "Access Denied" error on Assembly Loading
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