The server has encountered an error.
Access to the temp directory is denied. Identity under which XmlSerializer is running does not have sufficient permission to access the temp directory. CodeDom will use the user account the process is using to do the compilation, so if the user doesn't have access to system temp directory, you will not be able to compile. Use Path.GetTempPath() API to find out the temp directory location.
If you are getting the above error on Windows Server 2016 or any other Windows OS, this likely means that the operating system has configured with higher security so the ApplicationPoolIdentity, the account that Analyzer AppPoolInt (or AppPool for version prior to 3.0.2361) uses by default, does not have enough permission to access the temp directory or related folders.
To resolve this issue, you can either grant additional permissions to the ApplicationPoolIdentity account or by change the account to a local administrator account. You can check which account the AppPoolInt is using by to to IIS > Application Pools > AppPoolInt > Advanced Settings > Identity. Change it to a local administrator account should solve the issue.