Microsoft accidentally published the Windows Mobile 6.5 SDK (software developers kit) on Friday but has since pulled it, the company said.
Developers discovered the SDK on Microsoft's Download site. One, Joel Ivory Johnson, downloaded it and reports that it includes Widget tools and emulators for version 6.5.3, the next update to the OS.
He and another developer both had trouble using the SDK, indicating that it likely was not ready for release.
On Monday, a spokeswoman with Microsoft's public relations agency confirmed that it had been posted inadvertently. "While the SDK was not announced or promoted, it was discovered and generated questions from the community," she said. "To provide the best experience possible for Windows phone developers, the SDK will be reposted once final testing has been conducted."
Microsoft could be planning to release the SDK next month at the Mobile World Congress.
The first phones running Windows Mobile 6.5 became available late last year. Many expect that Microsoft will introduce Windows Mobile 7 at the Mobile World Congress next month with expectations that phones will go on sale some time this year.