1998 Cherokee Jeep Radio not accepting code?

Hi I have just purchased an old 1998 Cherokee Jeep Overis and cannot get the radio to accept the code.
I have been given a code but it keeps asking to repeat twice and then wait 2 hrs.
The previous owner promises it worked for him and there are no problems.

Please help if anyone can?

please email zak underscore iqbal5 at hotmail dot com