System.Threading.SemaphoreFullException: Adding the specified count to the semaphore would cause it to exceed its maximum count.

我确定重新启动IIS将“解决”的问题，但我想了解是什么原因，所以我可以确保它不会发生在我的生产网站。

堆栈跟踪的顶部是：

[SemaphoreFullException: Adding the specified count to the semaphore would cause it to exceed its maximum count.]
System.Threading.Semaphore.Release(Int32 releaseCount) +6065293
System.Data.ProviderBase.DbConnectionPool.PutNewObject(DbConnectionInternal obj) +57
System.Data.ProviderBase.DbConnectionPool.DeactivateObject(DbConnectionInternal obj) +338
System.Data.ProviderBase.DbConnectionPool.PutObject(DbConnectionInternal obj,Object owningObject) +163
System.Data.ProviderBase.DbConnectionInternal.CloseConnection(DbConnection owningObject,DbConnectionFactory connectionFactory) +117
System.Data.sqlClient.sqlInternalConnection.CloseConnection(DbConnection owningObject,DbConnectionFactory connectionFactory) +37
System.Data.sqlClient.sqlConnection.Close() +158
System.Web.DataAccess.sqlConnectionHolder.Close() +25
System.Web.Security.sqlRoleProvider.GetRolesForUser(String username) +847
System.Web.Security.RolePrincipal.IsInRole(String role) +182