Error: Ik tip cannot be connected to IK root

While following this:

Add an IK Solver constraint to lower_leg.r. Make the target foot.r in the object Armature. Alternative: a faster way to add an IK constraint is by selecting the Target (foot.r), then shift-selecting the bone (lower_leg.r) and pressing Ctrl i.
Change the ChainLen to 2.

from this url:

Any ideas why it doesnt work?

Well may be u did not disconnect the bone… as the target IK solver should not be the part of the chain … and also in the tutorial it says the leg.r should be child of none… i believe the problem you are facing is of connection of bones and child parent realtion… try to have the target IK bone be separate from the chain… well me too am not a advanced user but i believe this helped… if iam wrong then do correct me!!!