After a few Medline searches and imports, and then starting a new search, the medline search starts as usual, the search window opens and the bar on the bottom moves sideways, as it should. But forever (!). After closing JabRef and reopening it works again for a few times. This is really annoying.
I am using Ubuntu 9.10 and java * 2 /usr/lib/jvm/java-6-sun/jre/bin/java 63 manual Mode, and JabRef 2.5
Thank you for reporting this! It would be useful if you could check the error console (Help -> Show error console -> Choose the "Exceptions" tab) and see if it contains any error messages. Look at this after a failed medline search.