How to avoid "Unsupported major.minor version 49.0" error?

All my applets worked before, but now I get this error message from some of my applets:

java.lang.UnsupportedClassVersionError: PolarLotus (Unsupported major.minor version 49.0)

Check out Polar Lotus on

http://www.astralvisuals.com/Lotuses.htm

to see what I mean. What can I do do get rid of this and make the applet work again?

[360 byte] By [Eyvind3a] at [2007-11-26 15:30:03]