This bug was originally marked as duplicate of bug 144819, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.

Build: NetBeans IDE 7.4 (Build 201310111528)
VM: Java HotSpot(TM) 64-Bit Server VM, 23.25-b01, Java(TM) SE Runtime Environment, 1.7.0_25-b17
OS: Windows 8

User Comments:
GUEST: data base connection problem

GUEST: while doing 

select * from INFO on an thin oracle jdbc connection

GUEST: Opened 2 conection , one on mysql and one on db2 V9 express-c
View a table in mysql => ok

go on db2 and request view a table=> this error occurs

mebe: View table data in services-

emiddio: trying to view data of APP schema on a embedded driver url

jdbc:derby:C:\Sun\apache-openjpa-1.2.1-binary\apache-openjpa-1.2.1\examples\hellojpa\hellojpa-database

GUEST: Trying to run SQL statement against the Derby database shipped with Glassfish 3




Stacktrace: 
java.lang.IllegalStateException: This connection is not added to the ConnectionManager.
   at org.netbeans.api.db.explorer.ConnectionManager.showConnectionDialog(ConnectionManager.java:352)
   at org.netbeans.modules.db.sql.loader.SQLEditorSupport$SQLExecutor$1.run(SQLEditorSupport.java:555)
   at org.netbeans.modules.db.sql.loader.SQLEditorSupport$SQLExecutor$1.run(SQLEditorSupport.java:552)
   at org.openide.util.Mutex$1AWTWorker.run(Mutex.java:1386)
   at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:241)
   at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)