Oracle connection from Squirrel SQL
Your original connection string:

sqlplus64 "user/pw@pashratgdb01.lex.bb.com:1876/atgpen1.lex.bb.com"


This specifices atgpen1.lex.bb.com as a service name. The JDBC syntax you used specifies a SID. Service name identifies a service within a database. SID identifies an instance within a database. Those two are not the same.

Instead of this:

jdbc:oracle:thin:@pashratgdb01.lex.bb.com:1876:atgpen1.lex.bb.com"


Use this:

jdbc:oracle:thin:@//pashratgdb01.lex.bb.com:1876/atgpen1.lex.bb.com"