The vote which would have ousted veteran Tory MP Sir Patrick Cormack has been declared null and void.
Sir Patrick Cormack has been an MP since 1970
David Billson, chairman of Staffs South Conservatives, said there had been a "clerical error" and a fresh vote would be held in the next two or three weeks.
It follows claims there were more votes cast than people present at a meeting last week to decide the MP's future.
Sir Patrick, who was facing deselection after 33 years, described the development as "extraordinary".
Last Monday's vote went against Sir Patrick by a narrow margin but the voting figures remained secret even from the MP himself.
He said a party investigation had "established that the attendance record did not appear to reflect an accurate record of those entitled to vote and it has also revealed that more ballot papers were cast than people present".
Party chairman Francis Maude had written to Mr Billson saying it was "necessary" to declare the vote invalid, as it could potentially be challenged in court, he added.
Sir Patrick, who said he hoped the situation could be resolved "amicably," achieved the biggest swing to the Conservatives - 9.4% - at the last election.
But some members of his constituency association are thought to want a younger candidate to fight the next general election.
They are also thought to be unhappy that Sir Patrick did not feature the word "Conservative" prominently in his election literature.