.NET FOLLOWER

    The SharePoint is based on ASP.Net, so all possible ASP.Net errors may easily become apparent in a SharePoint application. The ‘Code blocks are not allowed in this file‘ issue isn’t an exception. To get rid of it we need to enable server side scripts by modifying the web.config file. Specifically we need to locate <PageParserPaths> within web.config and add a proper <PageParserPath> node to it. The following example demonstrates how to allow server side scripts for all pages, which contain the apps virtual folder in their relative paths:

<PageParserPaths>
    <PageParserPath VirtualPath="/apps/*" CompilationMode="Always" 
              AllowServerSideScript="true" IncludeSubFolders="true" />
</PageParserPaths>

After the modification, server side scripts will work for such pages as e.g.

http://myServer/apps/default.aspx
http://myServer/apps/appsubfolder1/MyPage.aspx (*)
http://myServer/apps/appsubfolder2/MyPage.aspx (*)
http://myServer/apps/appsubfolder2/subfolder3/MyPage.aspx (*)
and so on. 

Note that pages urls marked with asterisks (*) are eligible only if IncludeSubFolders is set to true.

To enable server side scripts for certain page, use something like this:

<PageParserPath VirtualPath="/apps/appsubfolder2/subfolder3/MyPage.aspx" 
              CompilationMode="Always" AllowServerSideScript="true" />