The Swedish Standards Institute (SIS) has invalidated this week's ballot on the proposed Office Open XML standard, eliminating one vote in favour of the standard currently being evaluated by the International Standards Organization (ISO).

The SIS said that it had received information that one of its members had cast more than one vote, invalidating the entire election.

As a result, the group will not be able to weigh in on the ISO procedure that seeks to establish Office Open XML as an open standard, as the deadline for votes to be registered passes on 2 September.

The Swedish election sparked widespread controversy earlier this week when the SIS approved Office Open XML. The standard competes with the Open Document Format backed by IBM, Sun Microsystems and most open source advocates.

A day before the meeting earlier this week, more than 20 companies suddenly paid a $1,300 membership fee that allowed them to vote. The large number of companies joining the SIS at the last minute raised suspicions.

The Office Open XML documentation is nearly 6,000 pages long, making it doubtful that the new members studied the proposed standard in detail.

Doubts were further raised when an email emerged in which Microsoft offered its partners "marketing contributions" if they joined the organisation and voted on the Office Open XML issue.

In a blog posting on Wednesday, Microsoft's director of corporate standards, Jason Matusow, admitted that two messages were sent, but stressed that the company immediately flagged them as a violation of company policy.

Microsoft called the two recipients asking them to ignore the message, and informed the SIS.

"Instructions from corporate to our regional teams around the world throughout this process have been to completely adhere to the rules of the national standards bodies, and that any party wishing to take part in the national standards body is directly responsible for paying any related fees," Matusow stated.

"This means partners must decide whether to participate and vote based on their own determination as to the importance of this standard to their business.

"To say it more directly, offers to pay standards participation fees are totally inconsistent with our internal policy."

Matusow pointed out that IBM had lobbied Swedish business partners to vote against the standard.

He also argued that companies joining SIS at the last minute is within the rules of the standards body, and that proponents, and opponents such as Google, joined.