Zambian immigration authorities on Friday blocked former president Rupiah Banda from leaving the country for the third time in nearly two months.
Banda, who is facing corruption charges, was stopped from boarding a flight to South Africa despite a High Court order releasing his passport.
"We did all the airport formalities but surprisingly an immigration officer came and said he had instructions from above not to allow president Banda to travel," his press aide Kennedy Limwanya told AFP.
"We showed him a court order but he still said he could not allow us."
Banda was set to fly to South Africa on a morning flight for a conference, after the High Court ruling on Thursday.
His planned trip has been marred by hiccups after a magistrate's court refused to return his passport, which he had to surrender after being re-arrested in April on corruption charges.
Banda, who ruled Zambia from 2008 to 2011, when he lost power to current President Michael Sata, has been appearing in court over a string of corruption allegations.
Parliament voted to strip him of his presidential immunity in February.
He was stopped from travelling to Kenya on April 9 to attend Uhuru Kenyatta's presidential inauguration, and last month was blocked from travelling to Ethiopia for an African Union summit.