What is wrong when E5 appears in window of the ACCU-Chek compact plus and how do you correct this?

E-5 indicates that the optical lens (reading lens is dirty). The lens is located where the strip ejects not exactly where the drum is located. The area will have a box with black and white dots and the lens is right underneath it. The manual does state alcohol can be used but it is better to apply a little water to a q-tip to clean and dry the lens.

Sometimes E-5 can also indicate that a strip is stuck in the unit.