Hy,
I upgrade ROS 4.1 to 4.2, after upgrade metarouter paniced! 
Regard Zsirmo
same problem here.
after downgrade to 3.30 the configuration was broken.
i did a /system reset
and configured the router again.
now it works again.
Ditto. This is the text that appeared on the console. supout.rif emailed to support referencing this post.
MikroTik 4.2
*munged*.com Login: BUG(1): exception in hypervisor 10000010!
pc=0xffffffff(00000000) ra=0xc000019c(00000000)
at=0x10000000 v0=0x00000001 v1=0x80002000
a0=0xc0373e30 a1=0x00000001 a2=0x00000010 a3=0x00000000
t0=0x00004000 t1=0xc020b194 t2=0x00000000 t3=0x00602021
t4=0x40835000 t5=0x00000000 t6=0x80248483 t7=0x0001800a
s0=0xc0373e30 s1=0xc037405f s2=0xc0370000 s3=0xc0104ba0
s4=0xafb00030 s5=0x8e230018 s6=0xafa20020 s7=0x8c790004
t8=0xc033bcc8 t9=0xffffffff k0=0xe0001b0c k1=0x8fbc0018
gp=0xc0370000 sp=0xc033bf58 s8=0x152200ba
BadVAddr=0xfffffffe Status=0x0800810b Cause=0x5000c010
supout.rif (emailed separately to support):
md5 07ebffcc83509dd36315dd658db520a2
sha1 812bef0f5b526f67ad2e171d68d72fdfc8f752c3