Hello, I performed an update from 4.4.1 to 4.9.3. I used the upgrade source and overwrote the site files then, modified the web.config, and ran the site. I did not receive any errors during the upgrade.

What should I do to fix this?

When I navigate to the site I get this error:

Here are the errors showing up in the error list 

Error 116 Type 'AuthenticationController' is not defined. 

Error 117 'ResetConfig' is not a member of 'System.Configuration.Configuration'. 

Error 118 Type 'DotNetNuke.Security.Authentication.Configuration' is not defined. 

Error 119 'AUTHENTICATION_KEY' is not a member of 'System.Configuration.Configuration'. 

Error 120 'UpdateConfig' is not a member of 'System.Configuration.Configuration'.

Error 126 Type 'DotNetNuke.Security.Authentication.AuthenticationController' is not defined.

Error 127 Type 'DotNetNuke.Security.Authentication.UserInfo' is not defined. 

Error 128 Type 'DotNetNuke.Security.Authentication.UserController' is not defined.

Error 129 Type 'DotNetNuke.Security.Authentication.AuthenticationController' is not defined.

[NullReferenceException: Object reference not set to an instance of an object.]
   DotNetNuke.Entities.Portals.PortalSettings.GetSiteSettings(Int32 PortalId) +91
   DotNetNuke.Entities.Portals.PortalSettings.GetSiteSetting(Int32 PortalId, String SettingName) +44
   DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) +5468
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +68
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75

4.4.1 to 4.9.3 is quite a jump.  Based on my personal experience and on what others have reported success/failure with in the forums, I'd recommend incremental upgrades from 4.4.1 to 4.6.2, 4.6.2 to 4.8.3, then 4.8.3 to 4.9.3.  Plenty of people have reported issues when trying to jump too far forward between versions (especially when starting from 4.6.x or earlier directly to 4.9.x).
 
Good luck-
-mamlin

I have never experienced this issue in the past, which authentication methods do you use?

If you are using AD provider, I'd suggest to uncomment it in web.config, remove the module from the installation and install new AD provider after you finished upgrade to current version.