If you're facing intermittent database connection to your fresh installed Oracle XE you may be victim of software counterfeiting. :D
ORA-12519, TNS:no appropriate service handler found The Connection descriptor used by the client was
Don't worry, I'm just kidding. I found it irritating at first time. provided search result from google, i found one simple solution.
This problem maybe because maximum number of processes allowed to run. Don't worry, just alter the database to allow maximum process.
1. type command below:
sqlplus "/as sysdba"
2. Enter this command:
SQL>ALTER SYSTEM SET PROCESSES=150 SCOPE=SPFILE;
3. Shutdown your database.
5. Wahlah! No more irritating ORA-12519!
PS: Bear in your blurry mind that this happen if you're connection exceed maximum connection. make sure you close your connection every time you have finished using it. (Sorry my bad English).