Yes solid coconut milk is bad and should be discarded.
When the coconut milk becomes chunky, solid or darkens in color or begins to curdle then the coconut mil has gone bad and should be thrown out and not used or consumed.
Drinking or consuming bad coconut milk could make you sick so if it seems bad throw it out and don't risk your health.
Also if the coconut milk smells sour or has a rancid smell to it then it's no longer good and should be thrown out.
Just like regular milk that becomes sour or chunky or hard then it's bad and needs to be discarded so that you don't get sick.