Are they both in the same location?
To add to what Kevin had said, are both scanners at the same location
and in the same room? If in the same room, are they side by side, or perhaps in different places in the room?
And which antenna are you using? The telescoping antenna that came with the scanners? Or something else. If the telescoping antennas are being used, are they extended the same length?
If the scanners are in the same room, but not side by side, try swapping locations, If the problem stays with the physical location (in your room or whatever), then it's likely being affected by simulcast. Simulcast issues are extremely location specific. Sometimes moving a scanner a foot or two makes all the difference between working, or not.