Numerous iPhone users are complaining that a software upgrade released Monday by Apple is causing a range of problems on their devices—from lost files to phones that no longer work at all.

"After updating to iOS 4 almost nothing works," reported a user who identified himself as Esnupe, on a support forum maintained by Apple. "I've lost my music, all my apps, and the gmail push ability. This is a complete disaster," said Esnupe.

Another user, M3G4UK, said the upgrade to iPhone OS 4 "bricked" his device. "First download failed with a 'Firmware Corrupt' error, so it downloaded again," wrote M3G4UK. "Now my iPhone is stuck in recovery mode," the user added.

Numerous others said the upgrade caused archived photos to appear blurry.

It's not uncommon for a major new software release to cause device problems—either due to bugs or user error. Vendors generally manage to sort out most problems within days by clarifying installation instructions or issuing a patch.

Also, many iPhone users said the upgrade to iOS 4 was smooth. "Mine took only a few minutes with zero problems," said Dgreen, in a post on Apple's support forum.

Apple released iOS 4 on Monday.

Many of the new features, such as multitasking, are designed to work with the new iPhone 4, which goes on sale in the U.S. on Thursday. The feature lets users engage in a number of tasks or activities simultaneously. For instance, they could listen to a Pandora music stream while using other third-party apps.

Multitasking also works with iPhone 3GS when upgraded to iOS 4.

iOS 4 also eases application organization through a feature that lets users create new folders simply by dragging one app icon on top of another of the same category, such as Games.

E-mail display has also been improved, as iPhone OS 4 offers a unified inbox that pulls together messages from all of a user's e-mail accounts. "With just a few taps, users can quickly switch between inboxes to see messages from any single account," according to Apple.

All told, iOS 4 offers more than 100 new features or enhancements. It can be downloaded from Apple's Web site or iTunes store. Apple said it plans to release a version of the software for the iPad tablet computer later this year.

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