The European Commission has Microsoft back in its sights over browser choices, as it reopens an investigation into whether the company is yet offering customers a fair choice of browser to use.
In 2009, the EC ruled that Microsoft must offer users a choice screen to allow them to choose their preferred web browser without having to wade through menu after menu in order to pick something other than IE.
Microsoft now says that "a technical error" was to blame for the missing choice.
"Due to a technical error, we missed delivering the BCS (browser choice screen) software to PCs that came with the service pack 1 update to Windows 7," it said in a statement.
"While we have taken immediate steps to remedy this problem, we deeply regret that this error occurred and we apologise for it."
"We take compliance with our decisions very seriously. And I trusted the company's reports were accurate," said Joaquin Almunia, VP of the Commission in charge of competition policy.
"But it seems that was not the case, so we have immediately taken action. If following our investigation, the infringement is confirmed, Microsoft should expect sanctions."
Microsoft was instructed to offer the choice screen rather than funnelling all Windows users directly to Internet Explorer in order to make the web browser market a more competitive place.
If the EC finds that Microsoft has failed to meet the agreed commitments, which it seems likely that it has, it may be fined up to 10 per cent of its total annual turnover.