STEPS TO REPRODUCE:
1. Install Netbeans on a window system
2. Install DB2 (we have it on an IBM mainframe)
3. Install DB2 Connect (we have Version 7.2 
FixPack4 with JDBC 2 enabled)
4. Establish Connection between the PC and DB2 
with the datbase name DB2ENTW (or what you want)
5. Start Netbeans IDE and add the database driver
5. From Runtime tab > expand to database node > 
right-click at the Drivers > select Add Driver
6. From the Add JDBC Driver dialog, click Add 
button > select the db2java.zip from the SQLLIB 
directory (D:/Programme/ibm/SQLLIB/java/)
   Driver Class:COM.ibm.db2.jdbc.app.DB2Driver 
should be selected
   > click Add - A new driver should have been 
created:"IBM DB2 (local)"
7. Now add a connection:Select the IBM DB2 
driver > right click > Connect Using > complete 
Database URL:jdbc:db2:DB2ENTW > enter DB 
username and password > click OK
8. NullPointerException occurs - but the 
connection could be established.
9. The tab changes from Basic setting to 
Advanced and a schema read from the db has to be 
selected. Select one and click OK.
10. Then the error message box appears 
with:Unable to add connection, cannot not 
establish a connection to jdbc:db2:db2entw using 
COM.ibm.db2.jdbc.app.DB2Driver 
(java.lang.UnsatisfiedLinkError: Native Library 
D:\Programme\ibm\SQLLIB\bin\db2jdbc.dll already 
loaded in another classloader)
Note: DB2 Connect only provides a JDBC Type 2 
driver.
This is maybe related with issue 42062.