We recently ran into the error below on our site collection that we worked around by turning off the output cache. We're going to be cleaning up ACLs some obvious areas where a workflow spins off unique permissions without removing prior permissions. But is there a real fix to the problem for MOSS 2007? It doesn't seem to be officially listed in the Software Boundaries document. We found out about it after our site kept erroring out. Thanks! Background: We were getting the following error: Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace: [ApplicationException: Attempt to release mutex not owned by caller. (Exception from HRESULT: 0x00000120)] System.Threading.ReaderWriterLock.ReleaseWriterLockInternal() +0 System.Threading.ReaderWriterLock.ReleaseWriterLock() +4 Microsoft.SharePoint.Publishing.ThreadSafeCache`2.ReleaseWriterLock() +26 Microsoft.SharePoint.Publishing.AclCache.LoadAllAcls(SPSite site) +343 Microsoft.SharePoint.Publishing.PublishingHttpModule.EnableCachingIfAppropriate(Object source, EventArgs e) +3352 System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64 Proposed solution from: http://blogs.msdn.com/spfargo/archive/2009/01/08/attempt-to-release-mutex-not-owned-by-caller-exception-when-output-cache-is-enabled.aspxEric

Hi Eric, Thanks for posting! I am sorry for the inconvenience that may have caused you. A good news is that the issue is fixed in the April 2009 Cumulative Update or later. You could refer to KB 968859 for more information. When you try to browse to a site if the site collection has more than 10000 ACL cache entries, you receive the following error message: Attempt to release mutex not owned by caller. (Exception from HRESULT: 0x00000120) Please visit Updates Resource Center for SharePoint Products and Technologies to get the CUs to resolve your issue. Thanks! Lambert Qin TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com Sincerely, Lambert Qin Posting is provided "AS IS" with no warranties, and confers no rights.

Lambert,Thanks for your reply. So is there a recommended ACL limit per site collection? The software boundary document doesn't seem to address it.Thanks!EricEric

Hi Eric, Yes, there is a 64 KB ACL limitation. The limit to the users related with your own environment, it probably be in the span 1500-2000 members. See http://blogs.msdn.com/mattlind/archive/2007/11/02/sharepoint-indexing-limited-by-64-kb-acl-limit.aspx for more information. Lambert Qin TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com Sincerely, Lambert Qin Posting is provided "AS IS" with no warranties, and confers no rights.