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When trying to connect to a Derby database (which I created with Netbeans) with Runtime->Databases->Drivers->Apache Derby (Embedded) with the url jdbc:derby:/export/home/tmp/DB/AddressBook I get the message Unable to add connection, cannot establish a connection to jdbc:derby:/export/home/tmp/DB/AddressBook using org.apache.derby.jdbc.EmbeddedDriver (Failed to start database '/export/home/tmp/DB/AddressBook', se the next exception for details.) There is no problem connecting to the same database with other tools, e.g. Derby's ij.
What version of Nb and what OS do you use? Are you able to reproduce in the latest Nb 5.0 dev build? It looks like currently fixed issue 63957.
I use NetBeans IDE Dev Build (200511221900) Linux 2.6.13-1.1532_FC4
Fixed. Checking in ConnectUsingDriverAction.java; /cvs/db/src/org/netbeans/modules/db/explorer/actions/ConnectUsingDriverAction.java,v <-- ConnectUsingDriverAction.javanew revision: 1.31; previous revision: 1.30 done I guess you have a db.lck file in your database directory. Remove it before you try to add the database to the Runtime tab.