Error When Creating a New Community from a Template

If creating a new community from a template shows the error An unexpected error occurred,Try again or contact your Salesforce administrator for help, compile all Apex classes: open Setup > Custom Code > Apex Classes and click Compile all classes. In a few minutes, the page displays the message Compilation Complete: Compilation Successful.

Find more information about compiling Apex classes in the Salesforce help article Manage Apex Classes.