After resuming the update to Samsung Windows phones on Wednesday, Microsoft is running into problems again.
Users on a Microsoft help forum are reporting that when they try to install the update, which was designed to improve the update function, they get an error code.
Microsoft is telling customers on Twitter that it is aware of the issue and is looking into it, and the company advises users who have the problem not to try to install the update again.
"Sorry for your frustrations. We are working hard to make sure all WP7 experiences are as smooth as possible," Microsoft wrote to one user on Twitter.
Microsoft started rolling out the update -- the first for Windows Phone 7 devices -- in February. Rather than add features people have been waiting for like cut and paste, the update was designed to make the update process better.
However, Microsoft suspended the update process for Samsung phones in late February after users reported that it made their phones unusable. It later reported that one in 10 users who received an update notification were unable to successfully install the software, although in 5 percent of the cases that was because the user had a poor Internet connection or insufficient computer storage space, Microsoft said.
On Wednesday when it started pushing out the update again to Samsung phones, Microsoft said company engineers had pinpointed the original problem and fixed it.