CRC is Cyclic Redundancy Check a test to be sure the packet sent is the same as the packet received, without line noise added in transit.
You may wish to be sure your DSL phone line inside your house is as new and as direct as possible (no extensions, if possible) past the demarc box, you are not allowed to replace parts, so if it is the phone company's line that adds the errors, you cannot effect them.
I tried to remain child-like, all I acheived was childish.