Popular Web applications Twitter and Google Calendar are having performance and availability problems, the companies said separately on Wednesday.
Google Calendar users started reporting difficulties logging into the service on Tuesday in its official discussion forum, but the company didn't acknowledge the issue until around 11 a.m. U.S. Eastern Time on Wednesday.
The inability to access their Google Calendar accounts is affecting "a significant subset of users," the company said in a note in its Google Apps Status Dashboard.
While Google finds a permanent fix for the bug, Calendar users can work around it by clearing their browser cookies or by signing out and then signing back into their accounts, the company said.
Meanwhile, late Wednesday morning microblogging and social-networking service Twitter began greeting an unspecified number of visitors to its home page with its "fail whale" error, saying the system is struggling under excess capacity. The problem is also affecting third-party Twitter applications.
Twitter officially acknowledged the issue at close to noon ET with a brief note on its Twitter Status blog, saying it is experiencing "site availability issues" and is working to solve them.
The issues follow a technical problem that affected Twitter's main site and third-party applications for about one hour on Tuesday.
Google's Postini hosted e-mail security suite also had performance problems on Tuesday and on Friday of last week, while the company's App Engine hosted application development platform has had recurrent performance problems with its datastore for weeks.
The software industry as a whole is moving to the cloud computing model, where vendors host applications for customers in their data centers, and away from the traditional approach of having customers install and maintain applications on their companies' premises.
However, questions about security and data-related regulatory compliance remain, as well as about the performance and availability of these vendor-hosted applications, especially those used in workplace settings that are important for organizations' operations, such as Postini.
In its note about the Google Calendar problems, Google made the point of specifying that organizations using Calendar as part of the Google Apps Premier suite aren't affected by this bug.
Premier is the Google Apps version designed for use by companies. It includes IT management and e-mail security controls, as well as a 99.9 percent uptime service level guarantee.
Twitter is a free service aimed at consumers, but it is used by many organizations to market and promote their services and products.