Error TNS already in use during datamart ETL

I've a production database environment 10.2.0.3 on SUSE linux. We have two databases running on the same oracle binaries. On the second database there is a datamart ETL job (Informatica) run globally by all the regions.

Since this past weekend, this job has been failing continuously, with the following error:

Message: Error connecting to database...

WRT_8001 [Session s_m_GAPositionStage Username datamart DB Error -1805

Database driver error...

Function Name : Logon

ORA-12542: TNS:address already in use

Database driver error...

Function Name : Connect
Database Error: Failed to connect to database using user [datamart] and connection string

This error is not thrown in any of the other jobs on this database or the other database.

In an effort to resolve this, we put in the parameter "queue_size" to 20 in listener.ora. But it failed again with the same error. Now I'm going to increase its value to 128 which is the default value of OS parameter SOMAXCONN at SUSE linux. There is another note which asks to add a listener port in this situation. Do you think queuesize can do it or should I add a new port? The current listener port is 1526 and is using a non-default listener.

Since this is the production box I've to resolve it ASAP as business is getting effected.

Any expert opinion folks??

Thanks for the help

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