Hi Sven,
Thank you for installing the Boa plugin for Eclipse. I'm sorry to hear that you are experiencing a problem with running Boa programs.
The Boa plugin uses the Equinox security bundle to store credentials in a safe and encrypted form. Based on your description, it seems that the plugin is unable to retain your credentials after having you provide them. Normally this would occur because empty, null, or extremely long (over 1 kilobyte) usernames/passwords have been entered. This doesn't sound like your situation, however, so I'd like to request the following information.
Could you please relay any errors appearing in the Eclipse Problems View ("Window" > "Show View" > "Problems"). Additionally, if you know you've installed a plugin in the past that utilizes Equinox, please let us know.