The problem has seen slots given ahead of the recommended eight-week interval.
An investigation has been launched, although the fault is now said to have been fixed.
An NHS Forth Valley spokesperson said: “If you have a second dose Covid-19 vaccination appointment with us this week at one of our vaccination centres – please be aware that there should be a minimum of eight weeks between your first and second appointment.
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“We have been made aware that some people may have received an appointment for their second coronavirus vaccination ahead of the eight-week interval recommended by the Joint Committee on Vaccination and Immunisation.
“This has been caused by a temporary fault in the scheduling system which has since been rectified.
“We apologise to those affected. Please check the number of days between your appointment. If you are 55 days and under (not eight weeks yet) please do not attend your appointment.
“You can re-book your appointment online here or we will either offer you to walk into any of our clinics on your eighth week (56 days-62 days) or send you a new appointment for your eighth week.
“If you are immuno-suppressed and have an earlier second dose appointment for clinical reasons, please come along as planned.”