Microsoft shares fell on Thursday after it declined to dampen rumours that its new Windows Vista operating system might face fresh delays.
Vista has already been delayed
Its shares closed down 2% after a Microsoft executive appeared to avoid confirming the current January 2007 Vista release data for consumers.
Instead, Microsoft's Kevin Johnson said Vista would be shipped "when it is available".
He was speaking at the firm's annual financial analyst meeting.
Microsoft originally intended to release Vista - the first major update since Windows XP was introduced five years ago - in the second half of 2006.
Yet in March of this year it postponed the release until 2007, and last month Microsoft chairman Bill Gates predicted there was only an "80% chance" it would be shipped on time.
Mr Johnson, Microsoft's co-president of Microsoft's platforms and services unit, said: "We are going to ship the product when it is ready, and we are just going to take it milestone by milestone."
Goldman Sachs analyst Rick Sherlund said Mr Johnson appeared to be hesitating over the release date.
Vista will be available for corporate customers in November.
Mr Johnson also told the analyst meeting that Microsoft was on target to achieve revenues of between $14.3bn (£7.7bn) and $14.5bn (£7.8bn) in its current fiscal year.