Lightning 1.0b3pre 1.0b2 and Lightning 1.0b3pre (20110206) with Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.15pre) Gecko/20110207 Lanikai/3.1.9pre. Steps to reproduce: 1. Create clean Thunderbird profile, install Lightning, restart 2. Switch to Calendar tab and close unifinder 3. Create event that is inside the unifinder filter range (e.g. next seven days) Actual results: Error: [Exception... "'[JavaScript Error: "this.tree is null" {file: "chrome://calendar/content/calendar-unifinder.js" line: 501}]' when calling method: [calIObserver::onAddItem]" nsresult: "0x80570021 (NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS)" location: "JS frame :: file:///.../calendar-js/calUtils.js :: notifyFunc :: line 1227" data: yes] STACK: 1: [file:///.../calendar-js/calUtils.js:1230] notifyFunc 2: [file:///.../calendar-js/calUtils.js:1233] calListenerBag_notify 3: [file:///.../modules/calProviderUtils.jsm:497] calObserverBag_notify 4: [file:///.../components/calCompositeCalendar.js:78] anonymous 5: [null:0] null 6: [file:///.../calendar-js/calUtils.js:1227] notifyFunc 7: [file:///.../calendar-js/calUtils.js:1233] calListenerBag_notify 8: [file:///.../modules/calProviderUtils.jsm:497] calObserverBag_notify 9: [file:///.../calendar-js/calStorageCalendar.js:455] cSC_adoptItem 10: [file:///.../calendar-js/calStorageCalendar.js:403] cSC_addItem Source file: file:///.../calendar-js/calUtils.js Line: 1230

Not sure if it has been reported somewhere, but it happens a similar error upon event modification e.g. by moving an event with drag and drop on any view. To reproduce it, the unifinder must be closed : Error: [Exception... "'[JavaScript Error: "this.tree is null" {file: "chrome://calendar/content/calendar-unifinder.js" line: 530}]' when calling method: [calIObserver::onModifyItem]" nsresult: "0x80570021 (NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS)" location: "JS frame :: resource://calendar/modules/calUtils.jsm -> file:///.../calendar-js/calUtils.js :: notifyFunc :: line 1236" data: yes] STACK: 1: [resource://calendar/modules/calUtils.jsm -> file:///.../calendar-js/calUtils.js:1239] notifyFunc 2: [resource://calendar/modules/calUtils.jsm -> file:///.../calendar-js/calUtils.js:1242] calListenerBag_notify 3: [resource://calendar/modules/calProviderUtils.jsm:502] calObserverBag_notify 4: [file:///.../components/calCompositeCalendar.js:85] null 5: [resource://calendar/modules/calUtils.jsm -> file:///.../calendar-js/calUtils.js:1236] notifyFunc 6: [resource://calendar/modules/calUtils.jsm -> file:///.../calendar-js/calUtils.js:1242] calListenerBag_notify 7: [resource://calendar/modules/calProviderUtils.jsm:502] calObserverBag_notify 8: [file:///.../components/calStorageCalendar.js:559] cSC_modifyItem 9: [resource://calendar/modules/calUtils.jsm -> file:///.../calendar-js/calTransactionManager.js:250] cT_doTransaction 10: [resource://calendar/modules/calUtils.jsm -> file:///.../calendar-js/calTransactionManager.js:83] cTM_createAndCommitTxn Source File: resource://calendar/modules/calUtils.jsm -> file:///.../calendar-js/calUtils.js Line: 1239 TB 8.0b3, Lightning 1.0rc1