As others have said, use System.IO.Directory.CreateDirectory.
But, you don't need to check if it exists first. From the documentation:
Any and all directories specified in path are created, unless they already exist or unless some part of path is invalid. If the directory already exists, this method does not create a new directory, but it returns a DirectoryInfo object for the existing directory.
I got this same error and got around it by doing 2 things.
Background:
I'm building a simple test ASP.Net application to try to work with Google API's OAuth2.0. I used "nuget" to install the Google.Apis.Calendar.v3 (v1.13.1.509) library, and it brought in a lot of other dlls that it depends on.
The Error:
When compiling a seemingly simple ASP.Net project targeting "Framework 4.5" on Visual Studio 2015 for Web (Express). The error showed itself in 2 ways:
I originally compiled the code using the Build command Ctrl+F5. Then I got a build error, but without a entry in the "Error" tab that normally would point to a source code line. (The project just would stop building). The output was:
------ Build started: Project: oauth2.pylogen.com, Configuration: Debug Any CPU ------
Validating Web Site
Building directory '/App_Code/'.
E:\Projects\oauth2.pylogen.com\App_Code\Google.Api.Pylogen\FlowMetadata.cs(26,13): error
CS0012: The type 'System.Object' is defined in an assembly that is not referenced. You
must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a'.
Validation Complete
========== Build: 0 succeeded or up-to-date, 1 failed, 0 skipped ==========
I then proceeded by installing the dotNet Framework 4.6.1 Developer Pack (the newest version that is not a preview).
Then I restarted VS 2015 for Web and got build again. This time I got an entry in the "Error" tab, that pointed to a source line:
flowInit.Scopes = new string[] { Google.Apis.Calendar.v3.CalendarService.Scope.Calendar };
When I commented out this line, the project build. I could pretty much do nothing about this line, but I just wanted to show the obscurity of the error!
Solutions:
After installing Framework 4.6.1 Developer Pack. I also added this line to Web.Config:
<compilation debug="true" targetFramework="4.5">
<assemblies>
<add assembly="System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>
</assemblies>
</compilation>
After this my project build completely. My assumption would be that Google is referring to the older System.Runtime.dll (although their Nuget package detail is showing that the target framework is 4.5).
Best Solution
Attempt 1:
A similar question was asked a couple of months back and look at those answers.
Attempt 2:
Have you cleared the "Temporary ASP.Net Files" for the site, usually found at C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files? There may be an old copy lingering around.