I just updated my 14w27b server to 14w28a
The server will after a short while (~20-30 secs) crash and spit out:

[17:55:59] [Server thread/ERROR]: Encountered an unexpected exception
u: Exception ticking world
at net.minecraft.server.MinecraftServer.x(SourceFile:582) ~[minecraft_se
rver.jar:?]
at pd.x(SourceFile:285) ~[minecraft_server.jar:?]
at net.minecraft.server.MinecraftServer.w(SourceFile:510) ~[minecraft_se
rver.jar:?]
at net.minecraft.server.MinecraftServer.run(SourceFile:426) [minecraft_s
erver.jar:?]
at java.lang.Thread.run(Unknown Source) [?:1.7.0_25]
Caused by: java.lang.IllegalArgumentException: Cannot get property bcl

Unknown macro: {name=age, clazz=class java.lang.Integer, values=[0, 1, 2, 3, 4, 5, 6, 7]}

as it does not
exist!
at bbw.b(SourceFile:91) ~[minecraft_server.jar:?]
at ayt.b(SourceFile:127) ~[minecraft_server.jar:?]
at ayt.c(SourceFile:69) ~[minecraft_server.jar:?]
at ary.b(SourceFile:416) ~[minecraft_server.jar:?]
at qg.h(SourceFile:373) ~[minecraft_server.jar:?]
at qg.c(SourceFile:199) ~[minecraft_server.jar:?]
at net.minecraft.server.MinecraftServer.x(SourceFile:578) ~[minecraft_se
rver.jar:?]
... 4 more
[17:55:59] [Server thread/ERROR]: This crash report has been saved to: C:\Users\
User\Desktop\Minecraft Server\.\crash-reports\crash-2014-07-09_17.55.59-server.t
xt