While Serato’s beat gridding system is quite flexible, it has some specific behavior that means not every grid coming from another app will be supported.
The main reason for this error message is usually that two or more grid markers are not placed 4 beats apart. When you analyze a track using ‘dynamic’ modes in another app or when you’ve beat gridded a track by hand and added extra markers to fix the grid, you may encounter this.
Serato support tracks with multiple grid markers and those can have multiple BPM values but they are required to be exactly 4 beats apart. To put this a different way, grid markers in Serato can only be placed on the first downbeat of every bar in the track.