It's not uncommon for 'free' products to run in 'full' mode (i.e. with all of their 'bells and whistles' - which you don't really need - running) for a short period and then revert to 'basic' mode thereafter. It's a way of demonstrating the full capabilities of the software and tempting you to buy the full version. In general, the fact that a program has reverted to 'basic' mode should not be a cause for concern. It will still do the essential part of its job perfectly well. (i.e. if your Kerio firewall has dropped down to a basic mode it should still be doing a perfectly good job as a firewall).
If you still want to switch to another free firewall, the one which most of the 'regulars, here on AB's Technology section, (including myself) use is Zone Alarm:
http://www.download.com/3000-2092-10039884.htm l
Chris