Error E01 or error E001 means that you started some procedure in one mode, but did not complete that procedure, and changed the mode switch to another mode. In order to resolve this error, you need to turn the key back to whatever mode you were using earlier, and complete (or cancel) whatever procedure that was previously started.
If you are unsure what mode you need to go to, then turn the key to all of the various modes. Aside from OFF or CAL, there should be one mode that does not give error E01/E001. Whichever mode does not give error E01/E001 is the correct mode that you need to use. Once the register is in the correct mode, you simply need to complete (or cancel) the procedure that was started earlier.