ORA-12518: TNS:listener could not hand off client connection ORACLE XE 11.2 x64
To understand the problem and try to fix it you need to check related logs: 
 listener.log, alert log, trace file, etc

possible causes and solutions:


listener problem:


Make sure there is no error message and listener is up and running by execute the following command:

lsnrclt status


if listener is down check the following it may help you troubleshoot this issue:


could be network error: check the even log for any network error and fix them.
service stopped or it has failure when trying to start:  start---&gt;run---&gt;services.msc the search for oracle listener service  should be like OracleInstancename  try to start it, if it failed to start it will throw an exception inside listener error and windows error number. please provide that error


listener workaround: 

add the following parameter to your listener:

DIRECT_HANDOFF_TTC_LISTENER=OFF





database problem:


1.database server memory were enough for new connection


database connection parameters such as: dedicated server, please checked processes parameter or query from v$resource_limit where resource_name=’processes’; checked max_utilization must less than Limit_value or shared server, verify large_pool_size or check dispatcher were enough for all connection.