When this error occurs you will see a big error message box instead of YAPI Dashboard. The error message will contain the error information similar to the following

System.Configuration.ConfigurationErrorsException: Configuration system failed to initialize ---> System.Configuration.ConfigurationErrorsException: Root element is missing. (C:\Users\op2\AppData\Local\Practical_Dental_Solution\yapidomain_Path_jidptpp2fspkqskwkdaw3l1rqkcg4ceb\\user.config) ---> System.Xml.XmlException: Root element is missing.
at System.Xml.XmlTextReaderImpl.Throw(Exception e)
at System.Xml.XmlTextReaderImpl.ThrowWithoutLineInfo(String res)
at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
at System.Xml.XmlTextReaderImpl.Read()
at System.Xml.XmlTextReader.Read()
at System.Configuration.XmlUtil..ctor(Stream stream, String name, Boolean readToFirstElement, ConfigurationSchemaErrors schemaErrors)
at System.Configuration.BaseConfigurationRecord.InitConfigFromFile()

Typically the cause of this error is an improper computer shutdown when someone turns off computer without shutting down Windows. Power failure is another possible cause.

Here is how you can restore YAPI configuration file.

Start Windows Explorer and navigate to the file listed inside a pair of round brackets ( ) in the error message. Delete the file. Start YAPI.  

You may notice that your local configuration has gone. Restore your local configuration via YAPI Dashboard.