After six yers of flawless use, a notice comes up

Replacement screen is required, so a new tv is probably cheaper.

Plasma screens are extremely susceptible to getting broken from any impacts to the face of the screen. What you are describing sound very much like distorted or dead pixels. It may not be a fixable issue, you may have to replace the entire unit or live with the purple bar. The reason you don't notice it as much when the screen is dark is because purple is on the darker end of the spectrum, and will be most visible in contrast to lighter ad brighter colors.

I have noticed a similar problem and after reading a circular that arrived through the post, I am beginning to suspect it is being caused by the new 4G mobile phone networks.

The circular offered a free filter to prevent such interference.

is there anything buy that has a magnet in it it demanatising screen move it away from screen or put on shelf were it not touching tv.

Is it an LCD tv or CRT ?
If CRT try moving the TV to a different location as the magnetic field from another device or even the earth can effect it.
The power switch (full power on) would normally demagnetise the screen.
If its an LCD has any object hit the screen, it could be a child's toy or knocking the screen can bruise the panel.

That's a vertical deflection issue. You can get replacement deflection boards from www.tvrepairworld.com the boards are remanufactured and have a full six month warranty and come with installation instructions on CD.

well u have stopped ur movies(dvds) to many times and the dots are burn marks on ur screens
if u read ur manual it will tell u NOT to leave a still picture on for to long as it will damage ur screen
i assume u have a PLASMA TELEVISION
if not... sorry cant help u

Sounds like a possible Bad Light Engine hopefully you have a extended warranty otherwise look for a costly repair

You have a completely different problem. The screen voltage for the blue picture tube is slightly too high on your set. This will put fine lines in the background of the picture, called retrace lines. This is very common and easy to correct. Remove the front speaker cover and the access panel behind it. Look inside and you will see a black box with six controls, each control having a little white glue on it. This is the Focus/Screen block. Three controls are labeled Focus and three are labeled Screen. The screen control in the center is for green but I am not sure if the screen control on the left or right is for blue for your model. With the TV on, set it to VIDEO 1 but do not connect anything to the VIDEO 1 jacks. This will produce a pure dark picture, showing any faint lines in the background. Choose one of the screen controls and increase (turn clockwise) it slightly. If the blue lines do not get brighter it means you are turning the red screen control, so put it back where it was and choose the other screen control. When you find the blue screen control, decrease (turn counter-clockwise) it until just when the blue lines are gone. If you want you can check that the red and green screen controls are set to just below the point where their faint lines are visible. When done, replace the panels and your picture will be back to perfect.

If it's a circular area you might be delaing with magnetism. Check the menu and there should be a control for geomagnetic correction and adjust accordingly.