connection timeout

We had a fully functional applet which retrieved and displayed data from 
an iSeries dbfile using certificate-authentication, jt400-toolbox and SQL. 
(all jar's are signed by same certificate). Now we noticed that this 
applet doesn't work anymore and returns following error:

java.sql.SQLException: The application requester cannot establish the 
connection.(Operation timed out: connect) 
 at com.ibm.as400.access.JDError.throwSQLException(JDError.java:480) 
 at 
com.ibm.as400.access.AS400JDBCConnection.setProperties(AS400JDBCConnection.java:2742)
 at 
com.ibm.as400.access.AS400JDBCDriver.prepareConnection(AS400JDBCDriver.java:807)
 at 
com.ibm.as400.access.AS400JDBCDriver.initializeConnection(AS400JDBCDriver.java:698)
 at com.ibm.as400.access.AS400JDBCDriver.connect(AS400JDBCDriver.java:285)
 at java.sql.DriverManager.getConnection(Unknown Source)
 at java.sql.DriverManager.getConnection(Unknown Source)
 at 
com.clipper.tools.CommunicateClipperJDBC.connect(CommunicateClipperJDBC.java:66)
 at com.clipper.objects.CompanyHeaders.connectToDB(CompanyHeaders.java:34)
 at 
com.clipper.objects.CompanyHeaders.getAllCompanyHeaders(CompanyHeaders.java:98)
 at bkhviews.ViewCompanyInfo.setFirmCMB(ViewCompanyInfo.java:531)
 at bkhviews.ViewCompanyInfo.createComponents(ViewCompanyInfo.java:160)
 at bkhviews.ViewCompanyInfo.init(ViewCompanyInfo.java:556)
 at sun.applet.AppletPanel.run(Unknown Source)
 at java.lang.Thread.run(Unknown Source)

When run from a browser at the office ('inside' the network), the applet 
works but when accessed from the users 'home'-PC, it refuses to work. 
Doesn't seems to be a firewall, security problem because all seems to be 
working util 'connection' is asked.

Any idea's, tips ?