One of those seeking to change its vote, the Netherlands, said it mistakenly thought the measure incorporated amendments approved by the European Parliament which excluded patents for pure software.
However, the vote had in fact approved a European Commission text which had not rejected these restrictions. Denmark, Germany, Poland and Portugal are also claiming their votes were mistaken.
The UK is in favour of the commission text, but Germany and others say that its all-embracing nature plays into the hands of big companies that might move in to patent the best software packages and kill off innovation by small software firms.
David Woods, IT and intellectual property lawyer at Masons, said although there was pressure from a wide range of interests, the directive was "getting there".
If present differences persist they will be settled through a conciliation process. Woods does not think it will come to that and believes a compromise solution will be found. The European Parliament will make its position known in September.