Skype, Microsoft Corp's online telephone and video service, said some users are unable to make calls on Monday because their settings show they and their contacts are off line, even when they are logged in.
In an updated blog post, Skype also said some messages to group chats are not being delivered and that users who are not already signed in may face difficulty while accessing their accounts.
Skype added that users could experience delays in seeing changes made to their accounts, such as credit balance and profile details.
Users also may face difficulty loading web pages on the Skype Community, the company said in a blog post. In an earlier post, Skype had said its instant messaging and Skype for Web services were not facing technical issues.