When installing or upgrading DotNetNuke, you may encounter an AspnetHostingPermission error e.g.
Exception Details: System.Security.SecurityException: Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=126.96.36.199, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below
Whilst this can occur because the machine is not setup to run asp.net (i.e. that permission has not been granted in a custom code access security policy), this is very unlikely. Instead what is more likely is that you are seeing an issue caused by a non-obvious security protection introduced by Microsoft in XP Service pack2.
Microsoft introduced the concept of marking files downloaded from an untrusted location (e.g. the internet) with a setting (called Zone.Identifier) and setting that value to be unsafe. To do so it uses alternative data streams so there is no change to the file contents itself. To remove this setting, right click the file (e.g. the install/upgrade zip file) and select properties and click "unblock". If there is no "unblock" button the file does not have this information.
Please note, this is a Microsoft protection added to code they control e.g. Internet explorer/Microsoft download manger etc. If you are using an alternative browser such as Firefox or Chrome they do not store zone information so this step is unnecessary. In addition, if you uncompress using a tool such as WinRAR (rather than Microsofts built in zip tool) this information will be ignored and not written to the individual files in the zip.