That error is simply stating your server is out of RAM/memory while trying to generate the page. The configured amount of 128M should be more than enough for almost any site, but if you have extra extensions that aren't required, they should be disabled. Additionally, if you have poorly coded 3rd party extensions or custom extensions, they could simply be using too much memory as well.
For reference, on this site, most pages take about 12M to render and at most 20M. JFBConnect adds about 5-10M per page. So, if this error just started happening, it's likely that you were already at the limits of your memory, and JFBConnect just happened to push you over.
If you want to check memory usage per page, you can enable the "System Debug" setting in the Global Configuration area of Joomla. At the bottom of each page, information about how it was loaded will be displayed. Try different pages and with different extensions enabled/disabled to try to narrow down the main culprit. If it happens to be JFBConnect, just let us know.
Hope that helps,
Alex