Lights, camera, action ... almost.

Although the Toronto international Film Festival doesn't officially open until Thursday, some are already missing out.

A computer glitch caused tickets to two world premieres — St. Vincent starring Bill Murray and The Drop starring James Gandolfini — to be oversold.

The festival's computer system failed to take two screenings off sale once they'd been sold out.

TIFF sent out a statement apologizing for the mix-up and offering customers exchanges and refunds.

"This is a one-off unanticipated glitch, that we hope will in no way alter an otherwise terrific experience at Festival 2014."