ORA-12520: TNS:listener could not find available handler for requested type of server

ISSUE:
cannot connect to database through listener though tnsping is good.

SYMTUM:
lsnrclt services

Service "TEST" has 1 instance(s).
  Instance "TEST", status READY, has 1 handler(s) for this service...
    Handler(s):
      "DEDICATED" established:704169 refused:0 state:blocked
         LOCAL SERVER

SOLUTION:
1.reloaded listener.
lsnrctl reload

2. register database instance

sqlplus / as sysdba

alter system register

reference:

http://www.orafaq.com/forum/t/60019/2/

https://forums.oracle.com/forums/thread.jspa?threadID=722511