The bug is related to caching, when the sites gets locked on random basis. Restarting the project can solve the issue, but the best option for you is to upgrade to our latest release as it includes many bugs fixed, new features and optimizations.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items