The ruling comes as Microsoft heads to Europe’s second-highest court, the Court of First Instance, to formally appeal the EC’s original 2004 antitrust ruling, in which it levied fines of $613bn.

The EC had ordered Microsoft to make available to rivals its code in order for non-Microsoft work group servers to run as well as Microsoft’s on Windows PC and servers.

To comply, Microsoft released technical information to its rivals, but computer science expert Neil Barrett, who was appointed by the EC as its monitoring trustee, said in his review that Microsoft’s documentation was inadequate.

As a result, the EC threatened Microsoft with potential daily fines of as much as $2.4m backdated to mid-December.

Microsoft had said correspondence between its rivals and the EC would have provided an insight into why Barrett’s reports were so scathingly critical.

Microsoft asserts there was collusion between Barrett and the EC, as well as its rivals, which is why it attempted to subpoena correspondence between the parties. The EC has not directly addressed Microsoft’s claims, but noted that Barrett was chosen from a list of potential reviewers that Microsoft has recommended.

Microsoft’s failure to subpoena sensitive documents from IBM was its latest setback in US courts. A US judge also recently rejected Microsoft’s attempts to subpoena documents from Novell Inc. In March, a US court also stymied Microsoft’s similar subpoena requests of Oracle Corp and Sun Microsystems Inc.

New York judge Colleen McMahon ruled that Microsoft’s attempts to subpoena documents from IBM were erroneous.

Microsoft hopes to discredit the reports on which the Commission relied by demonstrating that they were in whole or in part the results of efforts by IBM, a fierce Microsoft competitor, McMahon said in her ruling.

She said if Microsoft subpoenaed its rivals it would undermine sovereignty laws concerning US and foreign authorities. She also said the EC would be in possession of all the relevant documents that Microsoft seeks and that Microsoft should ask the EC for them.

The five-day hearing at a Luxembourg court will review Microsoft’s actions dating back to the late 1990s.

The EC’s ruling included allegations that by building video and audio players directly into its Windows operating system, Microsoft had prevented rival companies from selling media software of their own. In addition to fines, Microsoft was instructed by the EC to release a version of Windows that did not include its built-in media players.

Evidence from media player vendor RealNetworks Inc will be presented at the trial, as will systems compatibility evidence from IBM, Novell, Oracle and Sun.