Apart from potentially solving the wrong problem, one of the main concerns with writing a solution instead of a requirement is that technology is constantly changing. Solutions lock you into one technology or another, and whatever is chosen may be out of date by the time the product is built. By writing a requirement that does not include any technological component, you not only allow the designer to use the most appropriate, up-to-date technology, but also allow the product to change and adapt to new technologies as they emerge.
Link · 11. Non-functional Requirements