This error message occurs if you don't have sufficient permissions for writing to disk. Please check disk permissions of process used by application.
Could you please check unless you use SSL? You may see it when you edit content root -> Properties -> Security -> Requires SSL
If so, please configure it to “No” and check the live site. If it is all right now, you did not configure SSL properly. Please see this article for more information about SSL configuration on your server.
You can specify max file size by setting max request length parameter in the web.config file. Please open the web.config file, find the <system.web> section and insert the following line into it:
This will increase the max file size to 8MB. You can find more information at: http://msdn2.microsoft.com/en-us/library/e1f13641(vs.71).aspx.
Please see also The IIS6/7 is set by default to allow only 30MB files to be uploaded article.
Please see Installation on shared hosting server.
If you're using version before 2.2, you may receive an error message like this:
Exception Details: System.Security.SecurityException: Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=220.127.116.11, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.
You need to upgrade to version 2.2 and adjust the security settings as described in the KB article Kentico CMS in a Medium Trust Environment.