FDB,
I have not seen or heard of this message but in the absence of a definitive answer let us try and work it out. First we need more info, can you tell us the following?
1. What series of 737 was it and approx age?
2. What FMC update was it?
3. Do you have the IAN / GLS option enabled?
4. What airport, arrival & approach was in the FMC?
5. What freq was selected in Nav 1 & 2?
6. Where were you overflying at the time of the message?
7. Have you or your colleagues seen this message before, if so what were the circumstances & what was the fix?
BTW, if this message is not documented in your company FCOMs then you should inform your Fleet/Tech Captain who will see that it is or issue some guidance.
S&L