Using vmargs in eclipse.ini / jbdevstudio.ini which pointed to URLs that didn't exist, such as:

-vmargs
-Djboss.discovery.directory.url=http://download.jboss.org/jbosstools/discovery/nightly/earlyaccess/master/BAD-jbosstools-directory.xml
-Djboss.discovery.site.url=http://download.jboss.org/jbosstools/discovery/nightly/core/BAD-master/
-Djboss.discovery.earlyaccess.site.url=http://download.jboss.org/jbosstools/discovery/nightly/earlyaccess/BAD-master/

... I was able to get this error message in JBDS 8 Beta2:

Problems:

a) copy is squished into a narrow field - should fill the whole screen
b) "Web" is capitalized.
c) Rather than just saying "you may have a Web connection issue" how about linking the user to the proxy preferences page?