It is not blocked, but it does not match what the scanner believes the step size (12.5 kHz or 0.0125 MHz) should be for that band of frequencies.
It can be bypassed if you turn on FlexStep in your Expert Settings menu. You can get to the Expert Settings menu using PROG - FUNC - F3 (GLOB). Use the down arrow until you reach FlexStep and set it to "FlexStep: On." You should then be able to program pretty much any frequency you want.
I do not normally monitor any rail frequencies, so I am curious what 928.10625 MHz would be used for.