ms 402 radio cassette suddenly will not hold stations in memory

hi,

suddenly got a problem, i do a manual search on the radio for the stations i want, have the correct frequency obtainable from the web for Kent area.

i press the buttons 1-6, on the number i want to store station, it then goes not mute, then sound comes back, telling me its stored, as the manual says 

I select FM1 do a manual search, find the station i want, say Radio Kent, press button 6, where i want it, sound goes to mute then comes back

all is good, i leave it overnight, switch radio on, it then starts scanning through different stations by itself

is there any way i can completely clear all radio stations and start off fresh ?

i am mystified, never happened before

can anyone help please ?

i know its the bog standard radio but its ok for me