We know that the iMessage BETA came down - so starting to reinstall iChat failed with the error message "the deinstallation program of the BETA version of iMessage failed causing a missing internet connection".
just using the simple automatic requested deinstallation mechanism from the Beta iMessage Apple program. It came after after starting Imessage. The warning window pops up and asking to install iChat again. (I have no options in upgrading to 10.8; I have to use 10.7.5.)