After a poor opening half Canvey took a 48th minute lead when Dwain Clarke swung in a free-kick from the right and Ben Chenery headed in an effort which crashed against the inside of the far post and rebounded into keeper Ryan Clarke's arms.
But eagle-eyed assistant Gavin Muge ruled that the effort had crossed the line. Chenery was the man whose header at Villa Park gave Canvey the FA Trophy when they beat Forest Green in the final in 2001.
Forest Green's reply was no less controversial. Striker Guy Madjo fired in a close-range effort and referee Gary Evettes ruled defender Jay Conroy had manhandled Alex Meechan in going for the loose ball after 69 minutes. Substitute Michael Brough stepped up to equalise from the spot.
There were early chances for both sides. After three minutes a cross from the left saw Dwain Clarke cross for leading scorer Lee Boylan to plant a header into Ryan Clarke's arms.
Sixty seconds later at the other end Madjo got on the end of a Mark Beesley free-kick from the right at the far post but headed against the bar.
Despite a couple of corners and free-kicks from dangerous areas following fouls on young striker Jason Hallett, Canvey were unable to make an early breakthrough.
Neither side were enjoying much luck in building attacking moves on a bumpy surface.
Forest Green were producing a much better performance than of late in a spell which had seen them take just two points from seven games. They had forced four corners by the 36th minute and, from the fourth, central defender Abdou Sall was inches away from getting a good headed connection.
Canvey forced their fourth corner two minutes before the break and visiting midfielder Darren Jones was forced into a vital clearance when Mario Noto fired in a dangerous ball.
Sall again caused problems at a Forest Green corner on the stroke of half-time but, as the ball bounced dangerously in the area, the referee gave the relieved hosts a free-kick.
After a very poor first half the game at last came to life three minutes into the second period when Canvey were awarded a free-kick wide on the right following a foul on Hallett.
Chenery's header put the Islanders ahead and he nearly grabbed a second after 59 minutes when he headed Noto's left-wing corner goalwards, but this time Ryan Clarke punched to safety.
Forest Green equalised on 69 minutes with Brough's penalty, and Canvey had their own spot-kick appeal turned down four minutes later when an effort from substitute Kezie Ibe appeared to be handled by Forest Green defender Sekani Simpson. The game was livening up now and Madjo fired a 20-yard effort just wide.
Canvey substitute Dave McGhee, booked along with the visiting side's Damon Searle after a skirmish, lifted a loose ball over the bar, but the afternoon ended with honours even.