Not necessarily. There are a few reasons that message comes up, and another scheduled visit is only one of them.
The most common explanation is simply that all the available time slots for that inmate have been booked, either by other approved visitors or by the facility itself for programming, counts, or other scheduled activities. Facilities limit the number of video visits an inmate can have in a given period, and once those slots are filled, the system blocks additional appointments.
It could also mean the inmate is in a restricted status, whether due to an incident report, a disciplinary sanction, or a temporary lockdown situation. When visitation privileges are suspended, the system often returns an unavailability message rather than explaining the reason.
Technical issues and scheduling windows are another factor. Many facilities only open video visit booking for specific upcoming days, and outside those windows the system may show nothing available even if future slots exist.
If you are consistently hitting this message and cannot get clarity, contact the facility directly and ask about the inmate's visitation status. That will tell you faster than anything else what is actually going on.