The following IL code seems to cause Reflector to error when decompiling into anything except IL. Removing the first three instructions lets it work again.
.maxstack 3
.locals init (
[0] int32 num)
L_0000: br L_0007
L_0005: pop
L_0006: ldc.i4.0
L_0007: rest of program here
.maxstack 3 .locals init ( [0] int32 num) L_0000: br L_0007 L_0005: pop L_0006: ldc.i4.0 L_0007: rest of program here